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SubjectRe: [PATCH] oprofile, powerpc: Handle events that raise an exception without overflowing
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.

> ---
> 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
>
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