linux-kernel - Re: [RFC -tip] perf, x86: Add PERF_COUNT_HW_NMI

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Date:	Thu, 23 Jun 2011 13:44:36 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Don Zickus <dzickus@...hat.com>
Cc:	Cyrill Gorcunov <gorcunov@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>, Lin Ming <ming.m.lin@...el.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Vince Weaver <vweaver1@...s.utk.edu>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [RFC -tip] perf, x86: Add PERF_COUNT_HW_NMI_WATCHDOG event v2

On Thu, Jun 23, 2011 at 1:40 PM, Don Zickus <dzickus@...hat.com> wrote:
> On Thu, Jun 23, 2011 at 03:07:06PM +0400, Cyrill Gorcunov wrote:
>> On Thu, Jun 23, 2011 at 01:54:39PM +0400, Cyrill Gorcunov wrote:
>> ...
>> > >
>> > > No new hidden event, just a x86_pmu + a per-arch callbacks.
>> >
>> > Looks quite good for me, Don? (i'll cook some draft patch for review meanwhile).
>> >
>> >     Cyrill
>>
>> Since we are going to make __weak linking anyway maybe something like below
>> fit even beter? (untested)
>
> I don't think the compiler knows what platform you are running on and may
> just blindly link your new p4 function for all x86s, which is probably not
> what you want.
>
Don, is right. You need the level of indirection I had in my outline patch.

You also don't need the:
+       if (wd_attr->type       != PERF_TYPE_HARDWARE ||
+          wd_attr->attr.config != PERF_COUNT_HW_CPU_CYCLES)
+               return;

In the p4 callback given you know your coming in for the watchdog.

> Cheers,
> Don
>
>>
>>       Cyrill
>> ---
>>  arch/x86/kernel/cpu/perf_event_p4.c |   26 ++++++++++++++++++++++++++
>>  kernel/watchdog.c                   |    3 +++
>>  2 files changed, 29 insertions(+)
>>
>> Index: linux-2.6.git/arch/x86/kernel/cpu/perf_event_p4.c
>> ===================================================================
>> --- linux-2.6.git.orig/arch/x86/kernel/cpu/perf_event_p4.c
>> +++ linux-2.6.git/arch/x86/kernel/cpu/perf_event_p4.c
>> @@ -705,6 +705,32 @@ static int p4_validate_raw_event(struct
>>       return 0;
>>  }
>>
>> +void hw_nmi_watchdog_set_attr(struct perf_event_attr *wd_attr)
>> +{
>> +     /*
>> +      * Watchdog ticks are special on Netburst, we use
>> +      * that named "non-sleeping" ticks as recommended
>> +      * by Intel SDM Vol3b.
>> +      */
>> +     if (wd_attr->type       != PERF_TYPE_HARDWARE ||
>> +        wd_attr->attr.config != PERF_COUNT_HW_CPU_CYCLES)
>> +             return;
>> +
>> +     wd_attr->type   = PERF_TYPE_RAW;
>> +     wd_attr->config =
>> +             p4_config_pack_escr(P4_ESCR_EVENT(P4_EVENT_EXECUTION_EVENT)             |
>> +                     P4_ESCR_EMASK_BIT(P4_EVENT_EXECUTION_EVENT, NBOGUS0)            |
>> +                     P4_ESCR_EMASK_BIT(P4_EVENT_EXECUTION_EVENT, NBOGUS1)            |
>> +                     P4_ESCR_EMASK_BIT(P4_EVENT_EXECUTION_EVENT, NBOGUS2)            |
>> +                     P4_ESCR_EMASK_BIT(P4_EVENT_EXECUTION_EVENT, NBOGUS3)            |
>> +                     P4_ESCR_EMASK_BIT(P4_EVENT_EXECUTION_EVENT, BOGUS0)             |
>> +                     P4_ESCR_EMASK_BIT(P4_EVENT_EXECUTION_EVENT, BOGUS1)             |
>> +                     P4_ESCR_EMASK_BIT(P4_EVENT_EXECUTION_EVENT, BOGUS2)             |
>> +                     P4_ESCR_EMASK_BIT(P4_EVENT_EXECUTION_EVENT, BOGUS3))            |
>> +             p4_config_pack_cccr(P4_CCCR_THRESHOLD(15) | P4_CCCR_COMPLEMENT          |
>> +                     P4_CCCR_COMPARE);
>> +}
>> +
>>  static int p4_hw_config(struct perf_event *event)
>>  {
>>       int cpu = get_cpu();
>> Index: linux-2.6.git/kernel/watchdog.c
>> ===================================================================
>> --- linux-2.6.git.orig/kernel/watchdog.c
>> +++ linux-2.6.git/kernel/watchdog.c
>> @@ -355,6 +355,8 @@ static int watchdog(void *unused)
>>
>>
>>  #ifdef CONFIG_HARDLOCKUP_DETECTOR
>> +void __weak hw_nmi_watchdog_set_attr(struct perf_event_attr *wd_attr) { }
>> +
>>  static int watchdog_nmi_enable(int cpu)
>>  {
>>       struct perf_event_attr *wd_attr;
>> @@ -371,6 +373,7 @@ static int watchdog_nmi_enable(int cpu)
>>       /* Try to register using hardware perf events */
>>       wd_attr = &wd_hw_attr;
>>       wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
>> +     hw_nmi_watchdog_set_attr(wd_attr);
>>       event = perf_event_create_kernel_counter(wd_attr, cpu, NULL, watchdog_overflow_callback);
>>       if (!IS_ERR(event)) {
>>               printk(KERN_INFO "NMI watchdog enabled, takes one hw-pmu counter.\n");
>
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