x86/cpu/amd: Enable the fixed Instructions Retired counter IRPERF
authorKim Phillips <kim.phillips@amd.com>
Wed, 19 Feb 2020 17:52:43 +0000 (18:52 +0100)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Fri, 28 Feb 2020 16:22:19 +0000 (17:22 +0100)
commite0253c4220246fcd97bf9a92c604c1e36bd06c86
tree8c1d30d1f2f677e0b66030dadc82003ba2fc274f
parent88e4901d3ebd394ba079ea26536b8500fbd8e68b
x86/cpu/amd: Enable the fixed Instructions Retired counter IRPERF

commit 21b5ee59ef18e27d85810584caf1f7ddc705ea83 upstream.

Commit

  aaf248848db50 ("perf/x86/msr: Add AMD IRPERF (Instructions Retired)
  performance counter")

added support for access to the free-running counter via 'perf -e
msr/irperf/', but when exercised, it always returns a 0 count:

BEFORE:

  $ perf stat -e instructions,msr/irperf/ true

   Performance counter stats for 'true':

             624,833      instructions
                   0      msr/irperf/

Simply set its enable bit - HWCR bit 30 - to make it start counting.

Enablement is restricted to all machines advertising IRPERF capability,
except those susceptible to an erratum that makes the IRPERF return
bad values.

That erratum occurs in Family 17h models 00-1fh [1], but not in F17h
models 20h and above [2].

AFTER (on a family 17h model 31h machine):

  $ perf stat -e instructions,msr/irperf/ true

   Performance counter stats for 'true':

             621,690      instructions
             622,490      msr/irperf/

[1] Revision Guide for AMD Family 17h Models 00h-0Fh Processors
[2] Revision Guide for AMD Family 17h Models 30h-3Fh Processors

The revision guides are available from the bugzilla Link below.

 [ bp: Massage commit message. ]

Fixes: aaf248848db50 ("perf/x86/msr: Add AMD IRPERF (Instructions Retired) performance counter")
Signed-off-by: Kim Phillips <kim.phillips@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537
Link: http://lkml.kernel.org/r/20200214201805.13830-1-kim.phillips@amd.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
arch/x86/include/asm/msr-index.h
arch/x86/kernel/cpu/amd.c