linux-kernel - Re: [PATCH] perf_events: improve DS/BTS/PEBS buffer allocation

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Date:	Mon, 13 Sep 2010 17:51:20 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Stephane Eranian <eranian@...gle.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, paulus@...ba.org,
	davem@...emloft.net, perfmon2-devel@...ts.sf.net,
	eranian@...il.com, robert.richter@....com,
	"markus.t.metzger" <markus.t.metzger@...el.com>
Subject: Re: [PATCH] perf_events: improve DS/BTS/PEBS buffer allocation

On Mon, Sep 13, 2010 at 05:41:16PM +0200, Peter Zijlstra wrote:
> On Mon, 2010-09-13 at 17:31 +0200, Stephane Eranian wrote:
> > On Mon, Sep 13, 2010 at 5:24 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> > > On Mon, 2010-09-13 at 17:20 +0200, Stephane Eranian wrote:
> > >
> > >> That is the case we the sizes you have chosen today. For DS, we
> > >> could round up to one page for now.
> > >
> > > Markus chose the BTS size, for PEBS a single page was plenty since we do
> > > single event things (although we could do multiple for attr.precise_ip <
> > > 2).
> > >
> > > For DS there's:
> > >  kmalloc_node(sizeof(struct ds), GFP_KERNEL | __GFP_ZERO, cpu_node(cpu));
> > >
> > Ok, let try again with alloc_pages_node() + kmalloc_node().
> > I think we can stick with kmalloc() for DS because we are far from
> > consuming a page.
> 
> Thing is, if you're really seeing allocation failures,
> alloc_pages_node() isn't going to help. And the problem is, these
> allocations aren't movable, so memory compaction and all the other fancy
> stuff aren't really going to help much :/
> 
> There was some talk about a function that should sync all of vmalloc
> space, but iirc it was broken for some configs.


Mathieu has posted a set of patches to support traps/faults in NMIs,
this has been followed by a discussion with Linus.

http://linux.derkeiler.com/Mailing-Lists/Kernel/2010-07/msg05222.html

I think they came with some patches to solve the problem, pushing all the
fixup code in the NMI area, but the discussion was preempted by holidays
and I suspect Mathieu is focusing on some other scheduler patches right now :)

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