Date: Mon, 23 Mar 2026 20:22:14 +0000 From: Mitchell Horne <mhorne@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Cc: Ali Mashtizadeh <mashti@uwaterloo.ca> Subject: git: 39515d8b623a - main - hwpmc: Use rdtsc instead of rdtscp for timestamps Message-ID: <69c1a0f6.18dce.494c23c4@gitrepo.freebsd.org>
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The branch main has been updated by mhorne: URL: https://cgit.FreeBSD.org/src/commit/?id=39515d8b623a2be39d0c42a537fd9a17c417ff6e commit 39515d8b623a2be39d0c42a537fd9a17c417ff6e Author: Ali Mashtizadeh <mashti@uwaterloo.ca> AuthorDate: 2026-03-23 20:21:21 +0000 Commit: Mitchell Horne <mhorne@FreeBSD.org> CommitDate: 2026-03-23 20:21:21 +0000 hwpmc: Use rdtsc instead of rdtscp for timestamps No need for a barrier here, we are inside an NMI handler and executing a number of serializing instructions with stronger semantics. Reducing this overhead will increase our maximum safe sampling rate. Tested by: Paulo Fragoso <paulo@nlink.com.br> Reviewed by: mhorne MFC after: 1 week Sponsored by: Netflix Pull Request: https://github.com/freebsd/freebsd-src/pull/2076 --- sys/dev/hwpmc/hwpmc_mod.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) diff --git a/sys/dev/hwpmc/hwpmc_mod.c b/sys/dev/hwpmc/hwpmc_mod.c index fb1fdf832398..6133b52b516f 100644 --- a/sys/dev/hwpmc/hwpmc_mod.c +++ b/sys/dev/hwpmc/hwpmc_mod.c @@ -818,11 +818,9 @@ pmc_force_context_switch(void) uint64_t pmc_rdtsc(void) { -#if defined(__i386__) || defined(__amd64__) - if (__predict_true(amd_feature & AMDID_RDTSCP)) - return (rdtscp()); - else - return (rdtsc()); +#if defined(__i386__) + /* Unfortunately get_cyclecount on i386 uses cpu_ticks. */ + return (rdtsc()); #else return (get_cyclecount()); #endifhome | help
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