linux-kernel - Re: [PATCH RFC 0/2] percpu_ida: Take into account CPU topology when stealing tags

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Message-ID: <20140422115629.GI11182@twins.programming.kicks-ass.net>
Date:	Tue, 22 Apr 2014 13:56:29 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Alexander Gordeev <agordeev@...hat.com>
Cc:	linux-kernel@...r.kernel.org, Kent Overstreet <kmo@...erainc.com>,
	Jens Axboe <axboe@...nel.dk>, Shaohua Li <shli@...nel.org>,
	Nicholas Bellinger <nab@...ux-iscsi.org>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH RFC 0/2] percpu_ida: Take into account CPU topology when
 stealing tags

On Wed, Mar 26, 2014 at 02:34:22PM +0100, Alexander Gordeev wrote:
> Hello,
> 
> This series is against 3.14.0-rc7.
> 
> It is amied to further improve 'percpu_ida' tags locality by taking
> into account system's CPU topology when stealing tags. That is try
> to steal from a CPU which is 'closest' to the stealing one.
> 
> I would not bother to post this, since on several system the change
> did not show any improvement, i.e. on such one:

There's is much lower level fruit to be had before doing something like
this.

  https://lkml.org/lkml/2014/1/23/257
  https://lkml.org/lkml/2014/1/23/329
  https://lkml.org/lkml/2014/1/23/343
  https://lkml.org/lkml/2014/1/23/354

I've not had time to revisit/finish them, but you should definitely
clean up the percpu_ida stuff and reduce existing contention before
going overboard.
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