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 <emun...@mgebm.net> > Cc: <sta...@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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