Date: Wed, 22 Aug 2012 20:22:55 +0000 (UTC) From: Jim Harris <jimharris@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r239591 - head/sys/sys Message-ID: <201208222022.q7MKMtEt092126@svn.freebsd.org>
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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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