linux-kernel - Re: [RFC PATCH 2/3 v2] perf: Implement Nehalem uncore pmu

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Message-ID: <AANLkTimzEDXzF=hMzmNCvsPok1kqxd0vjNKuYur_+J5L@mail.gmail.com>
Date:	Fri, 26 Nov 2010 13:15:16 +0800
From:	Lin Ming <lin@...g.vg>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	Lin Ming <ming.m.lin@...el.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>, Andi Kleen <andi@...stfloor.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [RFC PATCH 2/3 v2] perf: Implement Nehalem uncore pmu

On Tue, Nov 23, 2010 at 6:17 PM, Stephane Eranian <eranian@...gle.com> wrote:
> Lin,
>
> On Sun, Nov 21, 2010 at 1:01 PM, Lin Ming <ming.m.lin@...el.com> wrote:
>> +static void uncore_pmu_enable_all(void)
>> +{
>> +       u64 ctrl;
>> +
>> +       /*
>> +        * (0xFULL << 48): 1 of the 4 cores can receive NMI each time
>> +        * but we don't know which core will receive the NMI when overflow happens
>> +        */
>
> That does not sound right. If you set bit 48-51 to 1, then all 4 cores
> will receive EVERY
> interrupt, i.e., it's a broadcast. That seems to contradict your
> comment: 1 of the 4. Unless
> you meant, they all get the interrupt and one will handle it, the
> other will find nothing to
> process. But I don't see the atomic op that would make this true in
> uncore_handle_irq().

Stephane,

The interrupt model is strange, it behaves differently when HT on/off.

If HT is off, all 4 cores will receive every interrupt, i.e., it's a broadcast.

If HT is on, only 1 of the 4 cores will receive the interrupt(both
Threads in that core receive the interrupt),
and it can't be determined which core will receive the interrupt.

Did you ever observe this?

>
> I also think that if you want all processors to receive the
> interrupts, then the mask should
> be 0xff when HT is on. The manual is rather obscure on this, but it
> does make sense.

I tried to set the mask 0xff when HT is on, but kernel panics, because
the reserve bits are set.

Thanks,
Lin Ming

>
>
>> +       ctrl = ((1 << UNCORE_NUM_GENERAL_COUNTERS) - 1) | (0xFULL << 48);
>> +       ctrl |= MSR_UNCORE_PERF_GLOBAL_CTRL_EN_FC0;
>> +
>> +       /*
>> +        * Freeze the uncore pmu on overflow of any uncore counter.
>> +        * This makes unocre NMI handling easier.
>> +        */
>> +       ctrl |= MSR_UNCORE_PERF_GLOBAL_CTRL_PMI_FRZ;
>> +
>> +       wrmsrl(MSR_UNCORE_PERF_GLOBAL_CTRL, ctrl);
>> +}
>> +
> --
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