linux-kernel - Re: perf: Translating mmap2 ids into socket info?

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Date:	Wed, 22 Oct 2014 22:02:19 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Joe Mario <jmario@...hat.com>
Cc:	Don Zickus <dzickus@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, eranian@...gle.com,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Andi Kleen <andi@...stfloor.org>, jolsa@...hat.com,
	rfowles@...hat.com
Subject: Re: perf:  Translating mmap2 ids into socket info?

On Wed, Oct 22, 2014 at 02:09:35PM -0400, Joe Mario wrote:
> >Yes, kernel memory is directly addresses, you basically have a static
> >address->node mapping, it never changes.
> 
> For kernel addresses, is there a reason not to have it available in perf,
> especially when that knowledge is important to understanding a numa-related slowdown?

Dunno why that isn't exposed in sysfs.

> In our case, when we booted with one configuration, AIM ran fine.  When we
> booted another way, AIM's performance dropped 50%.  It was all due to the dentry
> lock being located on a different (now remote) numa node.
> 
> We used your dmesg approach to track down the home node in an attempt to understand
> what was different between the two boots.  But the problem would have been obvious
> if perf simply listed the home node info.

Or if you'd used more counters that track the node interconnect traffic
;-) There are a few simple ones that count local/remote type things
(offcore), but using the uncore counters you can track way more.
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