• Linus Torvalds's avatar
    Revert changes to convert to ->poll_mask() and aio IOCB_CMD_POLL · a11e1d43
    Linus Torvalds authored
    The poll() changes were not well thought out, and completely
    unexplained.  They also caused a huge performance regression, because
    "->poll()" was no longer a trivial file operation that just called down
    to the underlying file operations, but instead did at least two indirect
    calls.
    
    Indirect calls are sadly slow now with the Spectre mitigation, but the
    performance problem could at least be largely mitigated by changing the
    "->get_poll_head()" operation to just have a per-file-descriptor pointer
    to the poll head instead.  That gets rid of one of the new indirections.
    
    But that doesn't fix the new complexity that is completely unwarranted
    for the regular case.  The (undocumented) reason for the poll() changes
    was some alleged AIO poll race fixing, but we don't make the common case
    slower and more complex for some uncommon special case, so this all
    really needs way more explanations and most likely a fundamental
    redesign.
    
    [ This revert is a revert of about 30 different commits, not reverted
      individually because that would just be unnecessarily messy  - Linus ]
    
    Cc: Al Viro <viro@zeniv.linux.org.uk>
    Cc: Christoph Hellwig <hch@lst.de>
    Signed-off-by: 's avatarLinus Torvalds <torvalds@linux-foundation.org>
    a11e1d43
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