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

This commit is contained in:

Ali Mashtizadeh

2026-03-23 17:21:21 -03:00

committed by

Mitchell Horne

parent 47402c9422

commit 39515d8b62

1 changed files with 3 additions and 5 deletions

									
										sys/dev/hwpmc/hwpmc_mod.c
									
		+3
		-5
	
												View File
												
				@@ -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());

				#endif