Re: patch for restricted vPMU modes

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 23/11/15 11:08, Jan Beulich wrote:
>>>> On 21.11.15 at 06:32, <bgregg@netflix.com> wrote:
>> I've included the short patch below for Xen 4.6.0, which provides these
>> modes (it also fixes a minor copy-and-paste error with
>> core2_get_fixed_pmc_count(), which I believe was accessing the wrong
>> register). I am not a veteran Xen programmer, so please feel free to edit
>> or rewrite this patch. In case this email messes it up, it's also on:
>> https://github.com/brendangregg/Misc/blob/master/xen/xen-4.6.0-vpmu-filter.d 
>> iff
> Thanks for the contribution, but I'm sorry - this is not how things work.
> Unless someone else want to pick this up (and perhaps even then) the
> patch lacks proper attributes (like a Signed-off-by tag), should be
> against -unstable instead of any released version, and I don't think
> anyone's going to go grab it from a web page to apply (i.e. if you
> can't get your mail client to handle it properly when inlined, attach it
> in addition to inlining).
>
> See http://wiki.xenproject.org/wiki/Submitting_Xen_Project_Patches.
>
>> --- xen-4.6.0-clean/xen/arch/x86/cpu/vpmu_intel.c 2015-10-05
>> 07:33:39.000000000 -0700
>> +++ xen-4.6.0-brendan/xen/arch/x86/cpu/vpmu_intel.c 2015-11-20
>> 15:29:42.571781176 -0800
>> @@ -166,10 +166,10 @@
>>   */
>>  static int core2_get_fixed_pmc_count(void)
>>  {
>> -    u32 eax;
>> +    u32 edx;
>>
>> -    eax = cpuid_eax(0xa);
>> -    return MASK_EXTR(eax, PMU_FIXED_NR_MASK);
>> +    edx = cpuid_edx(0xa);
>> +    return MASK_EXTR(edx, PMU_FIXED_NR_MASK);
>>  }
> Without going into much detail on the actual patch, this caught my
> eye: Either you're fixing a pretty blatant bug here, or this change
> just can't be right. In the former case, such a fix should be
> submitted as a separate patch.

Blatent bug.  The number of fixed function perf counters is bits 4:0 of edx.

~Andrew