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SubjectRe: [PATCH] oprofile, powerpc: Handle events that raise an exception without overflowing
Eric B Munson wrote:
> On Mon, 23 May 2011, Eric B Munson wrote:
>
>> Commit 0837e3242c73566fc1c0196b4ec61779c25ffc93 fixes a situation on POWER7
>> where events can roll back if a specualtive event doesn't actually complete.
>> This can raise a performance monitor exception. We need to catch this to ensure
>> that we reset the PMC. In all cases the PMC will be less than 256 cycles from
>> overflow.
>>
>> This patch lifts Anton's fix for the problem in perf and applies it to oprofile
>> as well.
>>
>> Signed-off-by: Eric B Munson <emunson@mgebm.net>
>> Cc: <stable@kernel.org> # as far back as it applies cleanly
>
> I'd like to get this patch into mainline this merge window if at all possible.
Ack. I've been able to create a system hang profiling with speculative events on POWER7. This patch fixes that problem.

-Maynard

>
>> ---
>> arch/powerpc/oprofile/op_model_power4.c | 24 +++++++++++++++++++++++-
>> 1 files changed, 23 insertions(+), 1 deletions(-)
>>
>> diff --git a/arch/powerpc/oprofile/op_model_power4.c b/arch/powerpc/oprofile/op_model_power4.c
>> index 8ee51a2..e6bec74 100644
>> --- a/arch/powerpc/oprofile/op_model_power4.c
>> +++ b/arch/powerpc/oprofile/op_model_power4.c
>> @@ -261,6 +261,28 @@ static int get_kernel(unsigned long pc, unsigned long mmcra)
>> return is_kernel;
>> }
>>
>> +static bool pmc_overflow(unsigned long val)
>> +{
>> + if ((int)val < 0)
>> + return true;
>> +
>> + /*
>> + * Events on POWER7 can roll back if a speculative event doesn't
>> + * eventually complete. Unfortunately in some rare cases they will
>> + * raise a performance monitor exception. We need to catch this to
>> + * ensure we reset the PMC. In all cases the PMC will be 256 or less
>> + * cycles from overflow.
>> + *
>> + * We only do this if the first pass fails to find any overflowing
>> + * PMCs because a user might set a period of less than 256 and we
>> + * don't want to mistakenly reset them.
>> + */
>> + if (__is_processor(PV_POWER7) && ((0x80000000 - val) <= 256))
>> + return true;
>> +
>> + return false;
>> +}
>> +
>> static void power4_handle_interrupt(struct pt_regs *regs,
>> struct op_counter_config *ctr)
>> {
>> @@ -281,7 +303,7 @@ static void power4_handle_interrupt(struct pt_regs *regs,
>>
>> for (i = 0; i < cur_cpu_spec->num_pmcs; ++i) {
>> val = classic_ctr_read(i);
>> - if (val < 0) {
>> + if (pmc_overflow(val)) {
>> if (oprofile_running && ctr[i].enabled) {
>> oprofile_add_ext_sample(pc, regs, i, is_kernel);
>> classic_ctr_write(i, reset_value[i]);
>> --
>> 1.7.4.1
>>
>>
>>
>> _______________________________________________
>> Linuxppc-dev mailing list
>> Linuxppc-dev@lists.ozlabs.org
>> https://lists.ozlabs.org/listinfo/linuxppc-dev



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