Author: jimharris
Date: Wed Aug 22 20:22:55 2012
New Revision: 239591
URL: http://svn.freebsd.org/changeset/base/239591
Log:
Remove unncessary atomic operation when reading process flags in
PMC_PROC_IS_USING_PMCS macro.
Invocations of this macro are not synchronized with setting/clearing
of P_HWPMC flag, so the atomic operation here isn't needed. Removing
the atomic operation provides noticeable improvement (5-6%) on
some scheduler-intensive workloads with HWPMC_HOOKS enabled on an
8C Sandy Bridge Xeon system.
Sponsored by: Intel
Reviewed by: jhb
MFC after: 1 week
Modified:
head/sys/sys/pmckern.h
Modified: head/sys/sys/pmckern.h
==============================================================================
--- head/sys/sys/pmckern.h Wed Aug 22 20:07:10 2012 (r239590)
+++ head/sys/sys/pmckern.h Wed Aug 22 20:22:55 2012 (r239591)
@@ -201,8 +201,7 @@ do { \
/* Check if a process is using HWPMCs.*/
#define PMC_PROC_IS_USING_PMCS(p) \
- (__predict_false(atomic_load_acq_int(&(p)->p_flag) & \
- P_HWPMC))
+ (__predict_false(p->p_flag & P_HWPMC))
/* Check if a thread have pending user capture. */
#define PMC_IS_PENDING_CALLCHAIN(p) \
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