Re: perf: Translating mmap2 ids into socket info?

[Peter Zijlstra <peterz@infradead.org>]

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.