1. 24 Nov, 2015 1 commit
  2. 10 Nov, 2015 2 commits
  3. 07 May, 2015 2 commits
  4. 09 Mar, 2015 4 commits
    • Rik van Riel's avatar
      context_tracking: Export context_tracking_user_enter/exit · efc1e2c9
      Rik van Riel authored
      Export context_tracking_user_enter/exit so it can be used by KVM.
      Reviewed-by: 's avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Signed-off-by: 's avatarRik van Riel <riel@redhat.com>
      Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: Andy Lutomirski <luto@amacapital.net>
      Cc: Will deacon <will.deacon@arm.com>
      Cc: Marcelo Tosatti <mtosatti@redhat.com>
      Cc: Christian Borntraeger <borntraeger@de.ibm.com>
      Cc: Luiz Capitulino <lcapitulino@redhat.com>
      Cc: Paolo Bonzini <pbonzini@redhat.com>
      Signed-off-by: 's avatarFrederic Weisbecker <fweisbec@gmail.com>
      efc1e2c9
    • Rik van Riel's avatar
      context_tracking: Run vtime_user_enter/exit only when state == CONTEXT_USER · 19fdd98b
      Rik van Riel authored
      Only run vtime_user_enter, vtime_user_exit, and the user enter & exit
      trace points when we are entering or exiting user state, respectively.
      
      The KVM code in guest_enter and guest_exit already take care of calling
      vtime_guest_enter and vtime_guest_exit, respectively.
      
      The RCU code only distinguishes between "idle" and "not idle or kernel".
      There should be no need to add an additional (unused) state there.
      Reviewed-by: 's avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Signed-off-by: 's avatarRik van Riel <riel@redhat.com>
      Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: Andy Lutomirski <luto@amacapital.net>
      Cc: Will deacon <will.deacon@arm.com>
      Cc: Marcelo Tosatti <mtosatti@redhat.com>
      Cc: Christian Borntraeger <borntraeger@de.ibm.com>
      Cc: Luiz Capitulino <lcapitulino@redhat.com>
      Cc: Paolo Bonzini <pbonzini@redhat.com>
      Signed-off-by: 's avatarFrederic Weisbecker <fweisbec@gmail.com>
      19fdd98b
    • Rik van Riel's avatar
      context_tracking: Generalize context tracking APIs to support user and guest · 3aab4f50
      Rik van Riel authored
      Generalize the context tracking APIs to support various nature of
      contexts. This is performed by splitting out the mechanism from
      context_tracking_user_enter and context_tracking_user_exit into
      context_tracking_enter and context_tracking_exit.
      
      The nature of the context we track is now detailed in a ctx_state
      parameter pushed to these APIs, allowing the same functions to not just
      track kernel <> user space switching, but also kernel <> guest transitions.
      
      But leave the old functions in order to avoid breaking ARM, which calls
      these functions from assembler code, and cannot easily use C enum
      parameters.
      Reviewed-by: 's avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Signed-off-by: 's avatarRik van Riel <riel@redhat.com>
      Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: Andy Lutomirski <luto@amacapital.net>
      Cc: Will deacon <will.deacon@arm.com>
      Cc: Marcelo Tosatti <mtosatti@redhat.com>
      Cc: Christian Borntraeger <borntraeger@de.ibm.com>
      Cc: Luiz Capitulino <lcapitulino@redhat.com>
      Cc: Paolo Bonzini <pbonzini@redhat.com>
      Signed-off-by: 's avatarFrederic Weisbecker <fweisbec@gmail.com>
      3aab4f50
    • Frederic Weisbecker's avatar
      context_tracking: Rename context symbols to prepare for transition state · c467ea76
      Frederic Weisbecker authored
      Current context tracking symbols are designed to express living state.
      As such they are prefixed with "IN_": IN_USER, IN_KERNEL.
      
      Now we are going to use these symbols to also express state transitions
      such as context_tracking_enter(IN_USER) or context_tracking_exit(IN_USER).
      But while the "IN_" prefix works well to express entering a context, it's
      confusing to depict a context exit: context_tracking_exit(IN_USER)
      could mean two things:
      	1) We are exiting the current context to enter user context.
      	2) We are exiting the user context
      We want 2) but the reviewer may be confused and understand 1)
      
      So lets disambiguate these symbols and rename them to CONTEXT_USER and
      CONTEXT_KERNEL.
      Acked-by: 's avatarRik van Riel <riel@redhat.com>
      Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: Andy Lutomirski <luto@amacapital.net>
      Cc: Will deacon <will.deacon@arm.com>
      Cc: Marcelo Tosatti <mtosatti@redhat.com>
      Cc: Christian Borntraeger <borntraeger@de.ibm.com>
      Cc: Luiz Capitulino <lcapitulino@redhat.com>
      Cc: Paolo Bonzini <pbonzini@redhat.com>
      Signed-off-by: 's avatarFrederic Weisbecker <fweisbec@gmail.com>
      c467ea76
  5. 28 Oct, 2014 1 commit
    • Oleg Nesterov's avatar
      sched: stop the unbound recursion in preempt_schedule_context() · 009f60e2
      Oleg Nesterov authored
      preempt_schedule_context() does preempt_enable_notrace() at the end
      and this can call the same function again; exception_exit() is heavy
      and it is quite possible that need-resched is true again.
      
      1. Change this code to dec preempt_count() and check need_resched()
         by hand.
      
      2. As Linus suggested, we can use the PREEMPT_ACTIVE bit and avoid
         the enable/disable dance around __schedule(). But in this case
         we need to move into sched/core.c.
      
      3. Cosmetic, but x86 forgets to declare this function. This doesn't
         really matter because it is only called by asm helpers, still it
         make sense to add the declaration into asm/preempt.h to match
         preempt_schedule().
      Reported-by: 's avatarSasha Levin <sasha.levin@oracle.com>
      Signed-off-by: 's avatarOleg Nesterov <oleg@redhat.com>
      Signed-off-by: 's avatarPeter Zijlstra (Intel) <peterz@infradead.org>
      Cc: Alexander Graf <agraf@suse.de>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Cc: Christoph Lameter <cl@linux.com>
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
      Cc: Steven Rostedt <rostedt@goodmis.org>
      Cc: Peter Anvin <hpa@zytor.com>
      Cc: Andy Lutomirski <luto@amacapital.net>
      Cc: Denys Vlasenko <dvlasenk@redhat.com>
      Cc: Chuck Ebbert <cebbert.lkml@gmail.com>
      Cc: Frederic Weisbecker <fweisbec@gmail.com>
      Link: http://lkml.kernel.org/r/20141005202322.GB27962@redhat.comSigned-off-by: 's avatarIngo Molnar <mingo@kernel.org>
      009f60e2
  6. 14 Jun, 2014 1 commit
  7. 05 May, 2014 1 commit
  8. 02 Dec, 2013 1 commit
  9. 27 Sep, 2013 1 commit
  10. 25 Sep, 2013 1 commit
  11. 14 Aug, 2013 5 commits
    • Frederic Weisbecker's avatar
      context_tracking: User/kernel broundary cross trace events · 1b6a259a
      Frederic Weisbecker authored
      This can be useful to track all kernel/user round trips.
      And it's also helpful to debug the context tracking subsystem.
      Signed-off-by: 's avatarFrederic Weisbecker <fweisbec@gmail.com>
      Cc: Steven Rostedt <rostedt@goodmis.org>
      Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Borislav Petkov <bp@alien8.de>
      Cc: Li Zhong <zhong@linux.vnet.ibm.com>
      Cc: Mike Galbraith <efault@gmx.de>
      Cc: Kevin Hilman <khilman@linaro.org>
      1b6a259a
    • Frederic Weisbecker's avatar
      context_tracking: Optimize context switch off case with static keys · 73d424f9
      Frederic Weisbecker authored
      No need for syscall slowpath if no CPU is full dynticks,
      rather nop this in this case.
      Signed-off-by: 's avatarFrederic Weisbecker <fweisbec@gmail.com>
      Cc: Steven Rostedt <rostedt@goodmis.org>
      Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Borislav Petkov <bp@alien8.de>
      Cc: Li Zhong <zhong@linux.vnet.ibm.com>
      Cc: Mike Galbraith <efault@gmx.de>
      Cc: Kevin Hilman <khilman@linaro.org>
      73d424f9
    • Frederic Weisbecker's avatar
      context_tracking: Optimize guest APIs off case with static key · 48d6a816
      Frederic Weisbecker authored
      Optimize guest entry/exit APIs with static keys. This minimize
      the overhead for those who enable CONFIG_NO_HZ_FULL without
      always using it. Having no range passed to nohz_full= should
      result in the probes overhead to be minimized.
      Signed-off-by: 's avatarFrederic Weisbecker <fweisbec@gmail.com>
      Cc: Steven Rostedt <rostedt@goodmis.org>
      Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Borislav Petkov <bp@alien8.de>
      Cc: Li Zhong <zhong@linux.vnet.ibm.com>
      Cc: Mike Galbraith <efault@gmx.de>
      Cc: Kevin Hilman <khilman@linaro.org>
      48d6a816
    • Frederic Weisbecker's avatar
      context_tracking: Optimize main APIs off case with static key · ad65782f
      Frederic Weisbecker authored
      Optimize user and exception entry/exit APIs with static
      keys. This minimize the overhead for those who enable
      CONFIG_NO_HZ_FULL without always using it. Having no range
      passed to nohz_full= should result in the probes to be nopped
      (at least we hope so...).
      
      If this proves not be enough in the long term, we'll need
      to bring an exception slow path by re-routing the exception
      handlers.
      Signed-off-by: 's avatarFrederic Weisbecker <fweisbec@gmail.com>
      Cc: Steven Rostedt <rostedt@goodmis.org>
      Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Borislav Petkov <bp@alien8.de>
      Cc: Li Zhong <zhong@linux.vnet.ibm.com>
      Cc: Mike Galbraith <efault@gmx.de>
      Cc: Kevin Hilman <khilman@linaro.org>
      ad65782f
    • Frederic Weisbecker's avatar
      context_tracking: Ground setup for static key use · 65f382fd
      Frederic Weisbecker authored
      Prepare for using a static key in the context tracking subsystem.
      This will help optimizing the off case on its many users:
      
      * user_enter, user_exit, exception_enter, exception_exit, guest_enter,
        guest_exit, vtime_*()
      Signed-off-by: 's avatarFrederic Weisbecker <fweisbec@gmail.com>
      Cc: Steven Rostedt <rostedt@goodmis.org>
      Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Borislav Petkov <bp@alien8.de>
      Cc: Li Zhong <zhong@linux.vnet.ibm.com>
      Cc: Mike Galbraith <efault@gmx.de>
      Cc: Kevin Hilman <khilman@linaro.org>
      65f382fd
  12. 12 Aug, 2013 4 commits
    • Frederic Weisbecker's avatar
      nohz: Only enable context tracking on full dynticks CPUs · 2e709338
      Frederic Weisbecker authored
      The context tracking subsystem has the ability to selectively
      enable the tracking on any defined subset of CPU. This means that
      we can define a CPU range that doesn't run the context tracking
      and another range that does.
      
      Now what we want in practice is to enable the tracking on full
      dynticks CPUs only. In order to perform this, we just need to pass
      our full dynticks CPU range selection from the full dynticks
      subsystem to the context tracking.
      
      This way we can spare the overhead of RCU user extended quiescent
      state and vtime maintainance on the CPUs that are outside the
      full dynticks range. Just keep in mind the raw context tracking
      itself is still necessary everywhere.
      Signed-off-by: 's avatarFrederic Weisbecker <fweisbec@gmail.com>
      Cc: Steven Rostedt <rostedt@goodmis.org>
      Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Borislav Petkov <bp@alien8.de>
      Cc: Li Zhong <zhong@linux.vnet.ibm.com>
      Cc: Mike Galbraith <efault@gmx.de>
      Cc: Kevin Hilman <khilman@linaro.org>
      2e709338
    • Frederic Weisbecker's avatar
      context_tracking: Fix runtime CPU off-case · d65ec121
      Frederic Weisbecker authored
      As long as the context tracking is enabled on any CPU, even
      a single one, all other CPUs need to keep track of their
      user <-> kernel boundaries cross as well.
      
      This is because a task can sleep while servicing an exception
      that happened in the kernel or in userspace. Then when the task
      eventually wakes up and return from the exception, the CPU needs
      to know if we resume in userspace or in the kernel. exception_exit()
      get this information from exception_enter() that saved the previous
      state.
      
      If the CPU where the exception happened didn't keep track of
      these informations, exception_exit() doesn't know which state
      tracking to restore on the CPU where the task got migrated
      and we may return to userspace with the context tracking
      subsystem thinking that we are in kernel mode.
      
      This can be fixed in the long term if we move our context tracking
      probes on very low level arch fast path user <-> kernel boundary,
      although even that is worrisome as an exception can still happen
      in the few instructions between the probe and the actual iret.
      
      Also we are not yet ready to set these probes in the fast path given
      the potential overhead problem it induces.
      
      So let's fix this by always enable context tracking even on CPUs
      that are not in the full dynticks range. OTOH we can spare the
      rcu_user_*() and vtime_user_*() calls there because the tick runs
      on these CPUs and we can handle RCU state machine and cputime
      accounting through it.
      Signed-off-by: 's avatarFrederic Weisbecker <fweisbec@gmail.com>
      Cc: Steven Rostedt <rostedt@goodmis.org>
      Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Borislav Petkov <bp@alien8.de>
      Cc: Li Zhong <zhong@linux.vnet.ibm.com>
      Cc: Mike Galbraith <efault@gmx.de>
      Cc: Kevin Hilman <khilman@linaro.org>
      d65ec121
    • Frederic Weisbecker's avatar
      context_tracing: Fix guest accounting with native vtime · 2d854e57
      Frederic Weisbecker authored
      1) If context tracking is enabled with native vtime accounting (which
      combo is useless except for dev testing), we call vtime_guest_enter()
      and vtime_guest_exit() on host <-> guest switches. But those are stubs
      in this configurations. As a result, cputime is not correctly flushed
      on kvm context switches.
      
      2) If context tracking runs but is disabled on some CPUs, those
      CPUs end up calling __guest_enter/__guest_exit which in turn
      call vtime_account_system(). We don't want to call this because we
      run in tick based accounting for these CPUs.
      
      Refactor the guest_enter/guest_exit code such that all combinations
      finally work.
      Signed-off-by: 's avatarFrederic Weisbecker <fweisbec@gmail.com>
      Cc: Steven Rostedt <rostedt@goodmis.org>
      Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Borislav Petkov <bp@alien8.de>
      Cc: Li Zhong <zhong@linux.vnet.ibm.com>
      Cc: Mike Galbraith <efault@gmx.de>
      Cc: Kevin Hilman <khilman@linaro.org>
      2d854e57
    • Frederic Weisbecker's avatar
      sched: Consolidate open coded preemptible() checks · fbb00b56
      Frederic Weisbecker authored
      preempt_schedule() and preempt_schedule_context() open
      code their preemptability checks.
      
      Use the standard API instead for consolidation.
      Signed-off-by: 's avatarFrederic Weisbecker <fweisbec@gmail.com>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Li Zhong <zhong@linux.vnet.ibm.com>
      Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Steven Rostedt <rostedt@goodmis.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Borislav Petkov <bp@alien8.de>
      Cc: Alex Shi <alex.shi@intel.com>
      Cc: Paul Turner <pjt@google.com>
      Cc: Mike Galbraith <efault@gmx.de>
      Cc: Vincent Guittot <vincent.guittot@linaro.org>
      fbb00b56
  13. 19 Jun, 2013 1 commit
    • Steven Rostedt's avatar
      tracing/context-tracking: Add preempt_schedule_context() for tracing · 29bb9e5a
      Steven Rostedt authored
      Dave Jones hit the following bug report:
      
       ===============================
       [ INFO: suspicious RCU usage. ]
       3.10.0-rc2+ #1 Not tainted
       -------------------------------
       include/linux/rcupdate.h:771 rcu_read_lock() used illegally while idle!
       other info that might help us debug this:
       RCU used illegally from idle CPU! rcu_scheduler_active = 1, debug_locks = 0
       RCU used illegally from extended quiescent state!
       2 locks held by cc1/63645:
        #0:  (&rq->lock){-.-.-.}, at: [<ffffffff816b39fd>] __schedule+0xed/0x9b0
        #1:  (rcu_read_lock){.+.+..}, at: [<ffffffff8109d645>] cpuacct_charge+0x5/0x1f0
      
       CPU: 1 PID: 63645 Comm: cc1 Not tainted 3.10.0-rc2+ #1 [loadavg: 40.57 27.55 13.39 25/277 64369]
       Hardware name: Gigabyte Technology Co., Ltd. GA-MA78GM-S2H/GA-MA78GM-S2H, BIOS F12a 04/23/2010
        0000000000000000 ffff88010f78fcf8 ffffffff816ae383 ffff88010f78fd28
        ffffffff810b698d ffff88011c092548 000000000023d073 ffff88011c092500
        0000000000000001 ffff88010f78fd60 ffffffff8109d7c5 ffffffff8109d645
       Call Trace:
        [<ffffffff816ae383>] dump_stack+0x19/0x1b
        [<ffffffff810b698d>] lockdep_rcu_suspicious+0xfd/0x130
        [<ffffffff8109d7c5>] cpuacct_charge+0x185/0x1f0
        [<ffffffff8109d645>] ? cpuacct_charge+0x5/0x1f0
        [<ffffffff8108dffc>] update_curr+0xec/0x240
        [<ffffffff8108f528>] put_prev_task_fair+0x228/0x480
        [<ffffffff816b3a71>] __schedule+0x161/0x9b0
        [<ffffffff816b4721>] preempt_schedule+0x51/0x80
        [<ffffffff816b4800>] ? __cond_resched_softirq+0x60/0x60
        [<ffffffff816b6824>] ? retint_careful+0x12/0x2e
        [<ffffffff810ff3cc>] ftrace_ops_control_func+0x1dc/0x210
        [<ffffffff816be280>] ftrace_call+0x5/0x2f
        [<ffffffff816b681d>] ? retint_careful+0xb/0x2e
        [<ffffffff816b4805>] ? schedule_user+0x5/0x70
        [<ffffffff816b4805>] ? schedule_user+0x5/0x70
        [<ffffffff816b6824>] ? retint_careful+0x12/0x2e
       ------------[ cut here ]------------
      
      What happened was that the function tracer traced the schedule_user() code
      that tells RCU that the system is coming back from userspace, and to
      add the CPU back to the RCU monitoring.
      
      Because the function tracer does a preempt_disable/enable_notrace() calls
      the preempt_enable_notrace() checks the NEED_RESCHED flag. If it is set,
      then preempt_schedule() is called. But this is called before the user_exit()
      function can inform the kernel that the CPU is no longer in user mode and
      needs to be accounted for by RCU.
      
      The fix is to create a new preempt_schedule_context() that checks if
      the kernel is still in user mode and if so to switch it to kernel mode
      before calling schedule. It also switches back to user mode coming back
      from schedule in need be.
      
      The only user of this currently is the preempt_enable_notrace(), which is
      only used by the tracing subsystem.
      Signed-off-by: 's avatarSteven Rostedt <rostedt@goodmis.org>
      Signed-off-by: 's avatarPeter Zijlstra <peterz@infradead.org>
      Link: http://lkml.kernel.org/r/1369423420.6828.226.camel@gandalf.local.homeSigned-off-by: 's avatarIngo Molnar <mingo@kernel.org>
      29bb9e5a
  14. 31 May, 2013 1 commit
    • Frederic Weisbecker's avatar
      kvm: Move guest entry/exit APIs to context_tracking · 521921ba
      Frederic Weisbecker authored
      The kvm_host.h header file doesn't handle well
      inclusion when archs don't support KVM.
      
      This results in build crashes for such archs when they
      want to implement context tracking because this subsystem
      includes kvm_host.h in order to implement the
      guest_enter/exit APIs but it doesn't handle KVM off case.
      
      To fix this, move the guest_enter()/guest_exit()
      declarations and generic implementation to the context
      tracking headers. These generic APIs actually belong to
      this subsystem, besides other domains boundary tracking
      like user_enter() et al.
      
      KVM now properly becomes a user of this library, not the
      other buggy way around.
      Reported-by: 's avatarKevin Hilman <khilman@linaro.org>
      Reviewed-by: 's avatarKevin Hilman <khilman@linaro.org>
      Tested-by: 's avatarKevin Hilman <khilman@linaro.org>
      Signed-off-by: 's avatarFrederic Weisbecker <fweisbec@gmail.com>
      Cc: Steven Rostedt <rostedt@goodmis.org>
      Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Kevin Hilman <khilman@linaro.org>
      Cc: Marcelo Tosatti <mtosatti@redhat.com>
      Cc: Gleb Natapov <gleb@redhat.com>
      Signed-off-by: 's avatarIngo Molnar <mingo@kernel.org>
      521921ba
  15. 27 Jan, 2013 3 commits
    • Frederic Weisbecker's avatar
      cputime: Safely read cputime of full dynticks CPUs · 6a61671b
      Frederic Weisbecker authored
      While remotely reading the cputime of a task running in a
      full dynticks CPU, the values stored in utime/stime fields
      of struct task_struct may be stale. Its values may be those
      of the last kernel <-> user transition time snapshot and
      we need to add the tickless time spent since this snapshot.
      
      To fix this, flush the cputime of the dynticks CPUs on
      kernel <-> user transition and record the time / context
      where we did this. Then on top of this snapshot and the current
      time, perform the fixup on the reader side from task_times()
      accessors.
      Signed-off-by: 's avatarFrederic Weisbecker <fweisbec@gmail.com>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Li Zhong <zhong@linux.vnet.ibm.com>
      Cc: Namhyung Kim <namhyung.kim@lge.com>
      Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Steven Rostedt <rostedt@goodmis.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      [fixed kvm module related build errors]
      Signed-off-by: 's avatarSedat Dilek <sedat.dilek@gmail.com>
      6a61671b
    • Frederic Weisbecker's avatar
      cputime: Generic on-demand virtual cputime accounting · abf917cd
      Frederic Weisbecker authored
      If we want to stop the tick further idle, we need to be
      able to account the cputime without using the tick.
      
      Virtual based cputime accounting solves that problem by
      hooking into kernel/user boundaries.
      
      However implementing CONFIG_VIRT_CPU_ACCOUNTING require
      low level hooks and involves more overhead. But we already
      have a generic context tracking subsystem that is required
      for RCU needs by archs which plan to shut down the tick
      outside idle.
      
      This patch implements a generic virtual based cputime
      accounting that relies on these generic kernel/user hooks.
      
      There are some upsides of doing this:
      
      - This requires no arch code to implement CONFIG_VIRT_CPU_ACCOUNTING
      if context tracking is already built (already necessary for RCU in full
      tickless mode).
      
      - We can rely on the generic context tracking subsystem to dynamically
      (de)activate the hooks, so that we can switch anytime between virtual
      and tick based accounting. This way we don't have the overhead
      of the virtual accounting when the tick is running periodically.
      
      And one downside:
      
      - There is probably more overhead than a native virtual based cputime
      accounting. But this relies on hooks that are already set anyway.
      Signed-off-by: 's avatarFrederic Weisbecker <fweisbec@gmail.com>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Li Zhong <zhong@linux.vnet.ibm.com>
      Cc: Namhyung Kim <namhyung.kim@lge.com>
      Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Steven Rostedt <rostedt@goodmis.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      abf917cd
    • Frederic Weisbecker's avatar
      context_tracking: Add comments on interface and internals · 4eacdf18
      Frederic Weisbecker authored
      This subsystem lacks many explanations on its purpose and
      design. Add these missing comments.
      
      v4: Document function parameter to be more kernel-doc
      friendly, as per Namhyung suggestion.
      Reported-by: 's avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: 's avatarFrederic Weisbecker <fweisbec@gmail.com>
      Cc: Alessio Igor Bogani <abogani@kernel.org>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Cc: Chris Metcalf <cmetcalf@tilera.com>
      Cc: Christoph Lameter <cl@linux.com>
      Cc: Geoff Levand <geoff@infradead.org>
      Cc: Gilad Ben Yossef <gilad@benyossef.com>
      Cc: Hakan Akkan <hakanakkan@gmail.com>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Li Zhong <zhong@linux.vnet.ibm.com>
      Cc: Namhyung Kim <namhyung.kim@lge.com>
      Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Steven Rostedt <rostedt@goodmis.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Signed-off-by: 's avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      4eacdf18
  16. 26 Jan, 2013 1 commit
    • Frederic Weisbecker's avatar
      context_tracking: Export context state for generic vtime · 95a79fd4
      Frederic Weisbecker authored
      Export the context state: whether we run in user / kernel
      from the context tracking subsystem point of view.
      
      This is going to be used by the generic virtual cputime
      accounting subsystem that is needed to implement the full
      dynticks.
      Signed-off-by: 's avatarFrederic Weisbecker <fweisbec@gmail.com>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Li Zhong <zhong@linux.vnet.ibm.com>
      Cc: Namhyung Kim <namhyung.kim@lge.com>
      Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Steven Rostedt <rostedt@goodmis.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      95a79fd4
  17. 30 Nov, 2012 1 commit
    • Frederic Weisbecker's avatar
      context_tracking: New context tracking susbsystem · 91d1aa43
      Frederic Weisbecker authored
      Create a new subsystem that probes on kernel boundaries
      to keep track of the transitions between level contexts
      with two basic initial contexts: user or kernel.
      
      This is an abstraction of some RCU code that use such tracking
      to implement its userspace extended quiescent state.
      
      We need to pull this up from RCU into this new level of indirection
      because this tracking is also going to be used to implement an "on
      demand" generic virtual cputime accounting. A necessary step to
      shutdown the tick while still accounting the cputime.
      Signed-off-by: 's avatarFrederic Weisbecker <fweisbec@gmail.com>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Cc: H. Peter Anvin <hpa@zytor.com>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Steven Rostedt <rostedt@goodmis.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Li Zhong <zhong@linux.vnet.ibm.com>
      Cc: Gilad Ben-Yossef <gilad@benyossef.com>
      Reviewed-by: 's avatarSteven Rostedt <rostedt@goodmis.org>
      [ paulmck: fix whitespace error and email address. ]
      Signed-off-by: 's avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      91d1aa43