perf_counter, x86: Extend perf_counter Pentium M support

I've attached a patch to remove the Pentium M special casing of
EMON and as noticed at least with my Pentium M the hardware PMU
now works:

 Performance counter stats for '/bin/ls /var/tmp':

       1.809988  task-clock-msecs         #      0.125 CPUs
              1  context-switches         #      0.001 M/sec
              0  CPU-migrations           #	 0.000 M/sec
            224  page-faults              #	 0.124 M/sec
        1425648  cycles                   #    787.656 M/sec
         912755  instructions             #	 0.640 IPC

Vince suggested that this code was trying to address erratum
Y17 in Pentium-M's:

  http://download.intel.com/support/processors/mobile/pm/sb/25266532.pdf

But that erratum (related to IA32_MISC_ENABLES.7) does not
affect perfcounters as we dont use this toggle to disable RDPMC
and WRMSR/RDMSR access to performance counters. We keep cr4's
bit 8 (X86_CR4_PCE) clear so unprivileged RDPMC access is not
allowed anyway.

Cc: Vince Weaver <vince@deater.net>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@googlemail.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/arch/x86/kernel/cpu/perf_counter.c b/arch/x86/kernel/cpu/perf_counter.c
index bed1c4c2f25119693cff43c0a4902278092aefe0..7e346d4bc0fbdb9a9e97fdc7379002765506e2c6 100644 (file)
--- a/arch/x86/kernel/cpu/perf_counter.c
+++ b/arch/x86/kernel/cpu/perf_counter.c
@@ -1583,10 +1583,8 @@ static int p6_pmu_init(void)
                break;
        case 9:
        case 13:
-               /* for Pentium M, we need to check if PMU exist */
-               rdmsr(MSR_IA32_MISC_ENABLE, low, high);
-               if (low & MSR_IA32_MISC_ENABLE_EMON)
-                       break;
+               /* Pentium M */
+               break;
        default:
                pr_cont("unsupported p6 CPU model %d ",
                        boot_cpu_data.x86_model);