Re: [PATCH] oprofile: re-arm APIC_DM_NMI in ppro_check_ctrs()

Cyrill Gorcunov
2008-11-10T16:11:51Z

[Eric Dumazet - Mon, Nov 10, 2008 at 03:23:00PM +0100]
> Andi Kleen a écrit :
>> Eric Dumazet <dada1@cosmosbay.com> writes:
>>
>>> diff --git a/arch/x86/oprofile/op_model_ppro.c b/arch/x86/oprofile/op_model_ppro.c
>>> index 3f1b81a..716d26f 100644
>>> --- a/arch/x86/oprofile/op_model_ppro.c
>>> +++ b/arch/x86/oprofile/op_model_ppro.c
>>> @@ -69,7 +69,7 @@ static void ppro_setup_ctrs(struct op_msrs const * const msrs)
>>> int i;
>>> if (!reset_value) {
>>> - reset_value = kmalloc(sizeof(unsigned) * num_counters,
>>> + reset_value = kmalloc(sizeof(reset_value[0]) * num_counters,
>>
>> Thanks for tracking this down.
>>
>> But that still doesn't explain why 2.6.27 fails too?
>
> Desesperatly Seeking Oprofile, next round.
>
> I know *nothing* about APIC but spent few hours to try several tricks
> and finally found something.
>
> It solved my problem : oprofile can run several hours without
> any freeze of NMI on any core.
>
> # grep NMI /proc/interrupts
> NMI: 10902884 9635871 10333815 8372989 7971483 8298373 8877495 10206963 Non-maskable interrupts
> ...
> # grep NMI /proc/interrupts
> NMI: 15518834 14340713 15038694 13078235 12676585 13003394 13582115 14912146 Non-maskable interrupts
>
>
> Can anybody understand and explain what is happening ?
>
> Is it a software or hardware problem ?
>
> [PATCH] oprofile: re-arm APIC_DM_NMI in ppro_check_ctrs()
>
> While using oprofile on my HP BL460c G1, (two quad core intel E5450 CPU),
> I noticed that one CPU after the other could not get anymore NMI.
>
> After a while, all cores where blocked (ie not generating events for oprofile)
> I tried all major linux versions and all where affected by this freeze.
>
> I found that we have to re-arm APIC_DM_NMI *before* writing to MSR counter
> when we get event notification.
>
> Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
> arch/x86/oprofile/op_model_ppro.c | 8 +++++---
> 1 files changed, 5 insertions(+), 3 deletions(-)

| diff --git a/arch/x86/oprofile/op_model_ppro.c b/arch/x86/oprofile/op_model_ppro.c
| index 3f1b81a..7b142da 100644
| --- a/arch/x86/oprofile/op_model_ppro.c
| +++ b/arch/x86/oprofile/op_model_ppro.c
| @@ -132,13 +132,15 @@ static int ppro_check_ctrs(struct pt_regs * const regs,
| rdmsrl(msrs->counters[i].addr, val);
| if (CTR_OVERFLOWED(val)) {
| oprofile_add_sample(regs, i);
| + /*
| + * We need to unmask the apic vector *before*
| + * writing reset_value to msr counter
| + */
| + apic_write(APIC_LVTPC, APIC_DM_NMI);
| wrmsrl(msrs->counters[i].addr, -reset_value[i]);
| }
| }
|
| - /* Only P6 based Pentium M need to re-unmask the apic vector but it
| - * doesn't hurt other P6 variant */
| - apic_write(APIC_LVTPC, apic_read(APIC_LVTPC) & ~APIC_LVT_MASKED);
|
| /* We can't work out if we really handled an interrupt. We
| * might have caught a *second* counter just after overflowing

Hi Eric,

for the record

apic_write(APIC_LVTPC, APIC_DM_NMI);

is not just 'unmask' but also *zeroify* (not sure if I wrote this
word right :) all fields when the origianl code was just 'unmasking'
TPC register

apic_write(APIC_LVTPC, apic_read(APIC_LVTPC) & ~APIC_LVT_MASKED);

that is why apic_read() was in former.

- Cyrill -