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

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Date:	Sun, 21 Nov 2010 22:04:19 +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>,
	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 Sun, 2010-11-21 at 20:46 +0800, Andi Kleen wrote:
> >
> > 2. Uncore pmu NMI handling
> >
> > All the 4 cores are programmed to receive uncore counter overflow
> > interrupt. The NMI handler(running on 1 of the 4 cores) handle all
> > counters enabled by all 4 cores.
> 
> Really for uncore monitoring there is no need to use an NMI handler.
> You can't profile a core anyways, so you can just delay the reporting
> a little bit. It may simplify the code to not use one here
> and just use an ordinary handler.

OK, I can use on ordinary interrupt handler here.

> 
> In general since there is already much trouble with overloaded
> NMI events avoiding new NMIs is a good idea.
> 
> 
> 
> > +
> > +static struct node_hw_events *uncore_events[MAX_NUMNODES];
> 
> Don't declare static arrays with MAX_NUMNODES, that number can be
> very large and cause unnecessary bloat. Better use per CPU data or similar
> (e.g. with  alloc_percpu)

I really need is a per physical cpu data here, is alloc_percpu enough?

> 
> > +	/*
> > +	 * The hw event starts counting from this event offset,
> > +	 * mark it to be able to extra future deltas:
> > +	 */
> > +	local64_set(&hwc->prev_count, (u64)-left);
> 
> Your use of local* seems dubious. That is only valid if it's really
> all on the same CPU. Is that really true?

Good catch! That is not true.

The interrupt handler is running on one core and the
data(hwc->prev_count) maybe on another core.

Any idea to set this cross-core data?

> 
> > +static int uncore_pmu_add(struct perf_event *event, int flags)
> > +{
> > +	int node = numa_node_id();
> 
> this should be still package id

Understand, this is in my TODO.

> 
> > +	/* Check CPUID signatures: 06_1AH, 06_1EH, 06_1FH */
> > +	model = eax.split.model | (eax.split.ext_model << 4);
> > +	if (eax.split.family != 6 || (model != 0x1A && model != 0x1E && model !=
> > 0x1F))
> > +		return;
> 
> You can just get that from boot_cpu_data, no need to call cpuid

Nice, will use it.

> 
> > +#include <linux/perf_event.h>
> > +#include <linux/capability.h>
> > +#include <linux/notifier.h>
> > +#include <linux/hardirq.h>
> > +#include <linux/kprobes.h>
> > +#include <linux/module.h>
> > +#include <linux/kdebug.h>
> > +#include <linux/sched.h>
> > +#include <linux/uaccess.h>
> > +#include <linux/slab.h>
> > +#include <linux/highmem.h>
> > +#include <linux/cpu.h>
> > +#include <linux/bitops.h>
> 
> Do you really need all these includes?

Only

#include <linux/perf_event.h>
#include <linux/kprobes.h>
#include <linux/hardirq.h>
#include <linux/slab.h>

are needed.

Thanks for the comments.
Lin Ming


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