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From: Robert Watson <rwatson@FreeBSD.org>
Date: Fri, 29 Apr 2005 18:56:36 +0000 (UTC)
To: src-committers@FreeBSD.org, cvs-src@FreeBSD.org,
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X-FreeBSD-CVS-Branch: HEAD
Subject: cvs commit: src/sys/vm uma_core.c uma_int.h
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rwatson     2005-04-29 18:56:36 UTC

  FreeBSD src repository

  Modified files:
    sys/vm               uma_core.c uma_int.h 
  Log:
  Modify UMA to use critical sections to protect per-CPU caches, rather than
  mutexes, which offers lower overhead on both UP and SMP.  When allocating
  from or freeing to the per-cpu cache, without INVARIANTS enabled, we now
  no longer perform any mutex operations, which offers a 1%-3% performance
  improvement in a variety of micro-benchmarks.  We rely on critical
  sections to prevent (a) preemption resulting in reentrant access to UMA on
  a single CPU, and (b) migration of the thread during access.  In the event
  we need to go back to the zone for a new bucket, we release the critical
  section to acquire the global zone mutex, and must re-acquire the critical
  section and re-evaluate which cache we are accessing in case migration has
  occured, or circumstances have changed in the current cache.
  
  Per-CPU cache statistics are now gathered lock-free by the sysctl, which
  can result in small races in statistics reporting for caches.
  
  Reviewed by:    bmilekic, jeff (somewhat)
  Tested by:      rwatson, kris, gnn, scottl, mike at sentex dot net, others
  
  Revision  Changes    Path
  1.119     +120 -103  src/sys/vm/uma_core.c
  1.30      +0 -10     src/sys/vm/uma_int.h