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

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Date:	Wed, 24 Nov 2010 17:55:13 +0800
From:	Lin Ming <ming.m.lin@...el.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Andi Kleen <andi@...stfloor.org>, 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 Mon, 2010-11-22 at 01:44 +0800, Peter Zijlstra wrote:
> On Sun, 2010-11-21 at 22:04 +0800, Lin Ming wrote:
> > 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.
> 
> Does the hardware actually allow using a different interrupt source?
> 
> > > 
> > > 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?
> 
> Nah, simply manually allocate bits using kmalloc_node(), that's
> something I still need to fix in Andi's patches as well.

I'm writing this like AMD NB events allocation.

Thanks,
Lin Ming

> 
> > > > +	/*
> > > > +	 * 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?
> 
> IIRC you can steer the uncore interrupts (it has a mask somewhere)
> simply steer everything to the first cpu in the nodemask?
> 
> 
> 


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