Re: [PATCH v2 5/7] ARM: perf_event: Fully support Krait CPU PMU events

[Stephen Boyd]

On 01/21/14 10:07, Will Deacon wrote:
> Hi Stephen,
>
> Thanks for the updates. A few more comments inline.
>
> On Wed, Jan 15, 2014 at 05:55:33PM +0000, Stephen Boyd wrote:
>> Krait supports a set of performance monitor region event
>> selection registers (PMRESR) sitting behind a cp15 based
>> interface that extend the architected PMU events to include Krait
>> CPU and Venum VFP specific events. To use these events the user
>> is expected to program the region register (PMRESRn) with the
>> event code shifted into the group they care about and then point
>> the PMNx event at that region+group combo by writing a
>> PMRESRn_GROUPx event. Add support for this hardware.
>>
>> Note: the raw event number is a pure software construct that
>> allows us to map the multi-dimensional number space of regions,
>> groups, and event codes into a flat event number space suitable
>> for use by the perf framework.
> [...]
>
>> +static u32 krait_read_pmresrn(int n)
>> +{
>> +       u32 val;
>> +
>> +       switch (n) {
>> +       case 0:
>> +               asm volatile("mrc p15, 1, %0, c9, c15, 0" : "=r" (val));
>> +               break;
>> +       case 1:
>> +               asm volatile("mrc p15, 1, %0, c9, c15, 1" : "=r" (val));
>> +               break;
>> +       case 2:
>> +               asm volatile("mrc p15, 1, %0, c9, c15, 2" : "=r" (val));
>> +               break;
>> +       default:
>> +               BUG(); /* Should be validated in krait_pmu_get_event_idx() */
>> +       }
>> +
>> +       return val;
>> +}
>> +
>> +static void krait_write_pmresrn(int n, u32 val)
>> +{
>> +       switch (n) {
>> +       case 0:
>> +               asm volatile("mcr p15, 1, %0, c9, c15, 0" : : "r" (val));
>> +               break;
>> +       case 1:
>> +               asm volatile("mcr p15, 1, %0, c9, c15, 1" : : "r" (val));
>> +               break;
>> +       case 2:
>> +               asm volatile("mcr p15, 1, %0, c9, c15, 2" : : "r" (val));
>> +               break;
>> +       default:
>> +               BUG(); /* Should be validated in krait_pmu_get_event_idx() */
>> +       }
>> +}
> Do you need isbs to ensure the pmresrn side-effects have happened, or are
> the registers self-synchronising? Similarly for your other IMP DEF
> registers.

There aren't any isbs in the downstream android sources so I assume
they're self synchronizing. I'll confirm with the CPU designers to make
sure.

>
>> +static void krait_pre_vpmresr0(u32 *venum_orig_val, u32 *fp_orig_val)
>> +{
>> +       u32 venum_new_val;
>> +       u32 fp_new_val;
>> +
>> +       /* CPACR Enable CP10 and CP11 access */
>> +       *venum_orig_val = get_copro_access();
>> +       venum_new_val = *venum_orig_val | CPACC_SVC(10) | CPACC_SVC(11);
>> +       set_copro_access(venum_new_val);
>> +
>> +       /* Enable FPEXC */
>> +       *fp_orig_val = fmrx(FPEXC);
>> +       fp_new_val = *fp_orig_val | FPEXC_EN;
>> +       fmxr(FPEXC, fp_new_val);
> Messing around with the lot (especially with kernel-mode neon now in
> mainline) does scare me. I'd like some BUG_ON(preemptible()) and you could
> consider using kernel_neon_{begin,end} but they're a lot heavier than you
> need (due to non-lazy switching)
>
> Finally, I'd really like to see this get some test coverage, but I don't
> want to try running mainline on my phone :) Could you give your patches a
> spin with Vince's perf fuzzer please?
>
>   https://github.com/deater/perf_event_tests.git
>
> (then build the contents of the fuzzer directory and run it for as long as
> you can).
>

Ok. I'll see what I can do.

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