tree e750143e578503b77a66eff21595b16730506802
parent 9f4a6dce10941380ad7365cc9b0ef038ed56cbf9
author Alex Williamson <alex.williamson@hp.com> 1126045024 -0700
committer Linus Torvalds <torvalds@g5.osdl.org> 1126137444 -0700

[PATCH] optimize writer path in time_interpolator_get_counter()

      Christoph Lameter <clameter@engr.sgi.com>

When using a time interpolator that is susceptible to jitter there's
potentially contention over a cmpxchg used to prevent time from going
backwards.  This is unnecessary when the caller holds the xtime write
seqlock as all readers will be blocked from returning until the write is
complete.  We can therefore allow writers to insert a new value and exit
rather than fight with CPUs who only hold a reader lock.

Signed-off-by: Alex Williamson <alex.williamson@hp.com>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>