• Paul E. McKenney's avatar
    rcu: Rename cond_resched_rcu_qs() to cond_resched_tasks_rcu_qs() · cee43939
    Paul E. McKenney authored
    Commit e31d28b6 ("trace: Eliminate cond_resched_rcu_qs() in favor
    of cond_resched()") substituted cond_resched() for the earlier call
    to cond_resched_rcu_qs().  However, the new-age cond_resched() does
    not do anything to help RCU-tasks grace periods because (1) RCU-tasks
    is only enabled when CONFIG_PREEMPT=y and (2) cond_resched() is a
    complete no-op when preemption is enabled.  This situation results
    in hangs when running the trace benchmarks.
    
    A number of potential fixes were discussed on LKML
    (https://lkml.kernel.org/r/20180224151240.0d63a059@vmware.local.home),
    including making cond_resched() not be a no-op; making cond_resched()
    not be a no-op, but only when running tracing benchmarks; reverting
    the aforementioned commit (which works because cond_resched_rcu_qs()
    does provide an RCU-tasks quiescent state; and adding a call to the
    scheduler/RCU rcu_note_voluntary_context_switch() function.  All were
    deemed unsatisfactory, either due to added cond_resched() overhead or
    due to magic functions inviting cargo culting.
    
    This commit renames cond_resched_rcu_qs() to cond_resched_tasks_rcu_qs(),
    which provides a clear hint as to what this function is doing and
    why and where it should be used, and then replaces the call to
    cond_resched() with cond_resched_tasks_rcu_qs() in the trace benchmark's
    benchmark_event_kthread() function.
    Reported-by: 's avatarSteven Rostedt <rostedt@goodmis.org>
    Signed-off-by: 's avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
    Tested-by: 's avatarNicholas Piggin <npiggin@gmail.com>
    cee43939
torture.c 21 KB