linux-kernel - Re: [PATCH 1/4] perf, x86: Add Intel Nehalem/Westmere uncore pmu

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Date:	Mon, 04 Jul 2011 14:39:01 +0800
From:	Lin Ming <ming.m.lin@...el.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>,
	Stephane Eranian <eranian@...gle.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] perf, x86: Add Intel Nehalem/Westmere uncore pmu

On Fri, 2011-07-01 at 00:58 +0800, Andi Kleen wrote:
> On Thu, Jun 30, 2011 at 08:09:53AM +0000, Lin Ming wrote:
> > +static u64 uncore_perf_event_update(struct perf_event *event)
> > +{
> > +	struct hw_perf_event *hwc = &event->hw;
> > +	int shift = 64 - intel_uncore_pmu.cntval_bits;
> > +	u64 prev_raw_count, new_raw_count;
> > +	s64 delta;
> > +
> > +	/*
> > +	 * Careful: an NMI might modify the previous event value.
> 
> There are no NMIs without sampling, so at least the comment seems bogus.
> Perhaps the code could be a bit simplified now without atomics.

I'm not sure if uncore PMU interrupt need to be enabled for counting
only. What do you think?

> 
> > +static int uncore_pmu_event_init(struct perf_event *event)
> > +{
> > +	struct hw_perf_event *hwc = &event->hw;
> > +
> > +	if (!uncore_pmu_initialized)
> > +		return -ENOENT;
> > +
> > +	if (event->attr.type != uncore_pmu.type)
> > +		return -ENOENT;
> > +
> > +	/*
> > +	 * Uncore PMU does measure at all privilege level all the time.
> > +	 * So it doesn't make sense to specify any exclude bits.
> > +	 */
> > +	if (event->attr.exclude_user || event->attr.exclude_kernel
> > +	    || event->attr.exclude_hv || event->attr.exclude_idle)
> > +		return -ENOENT;
> > +
> > +	/* Sampling not supported yet */
> > +	if (hwc->sample_period)
> > +		return -EINVAL;
> 
> Don't we need a "is root" check here? uncore counts everything, so
> it cannot be limited to a single process.

Yes, will add a "is root" check.

Will add .task_ctx_nr = perf_invalid_context to disallow per-process
counting.

> 
> > +static void uncore_pmu_cpu_starting(int cpu)
> > +{
> > +	struct cpu_uncore_events *cpuc = &per_cpu(cpu_uncore_events, cpu);
> > +	struct intel_uncore *uncore;
> > +	int i, uncore_id;
> > +
> > +	if (boot_cpu_data.x86_max_cores < 2)
> > +		return;
> 
> Why that check? uncore counting should work on a single core system too.
> 
> I think you should remove all of those.

Agree, will remove it.

> 
> > +
> > +	uncore_id = topology_physical_package_id(cpu);
> > +	WARN_ON_ONCE(uncore_id == BAD_APICID);
> > +
> > +	raw_spin_lock(&intel_uncore_lock);
> 
> Does this really need to be a raw spinlock? 

I think spinlock is enough.

> 
> > +#define NHM_MSR_UNCORE_PERF_GLOBAL_CTRL    	0x391
> > +#define NHM_MSR_UNCORE_PMC0			0x3b0
> > +#define NHM_MSR_UNCORE_PERFEVTSEL0		0x3c0
> 
> These should be in msr-index.h

Will move these.

Thanks,
Lin Ming

> 
> 
> -Andi


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