Groups > linux.kernel > #1662058

Re: [RFC PATCH] sched: select_idle_core should select least utilized core

From	Peter Zijlstra <peterz@infradead.org>
Newsgroups	linux.kernel
Subject	Re: [RFC PATCH] sched: select_idle_core should select least utilized core
Date	2017-06-09 10:00 +0200
Message-ID	<tQmZP-7c4-7@gated-at.bofh.it> (permalink)
References	<tQbi2-8li-27@gated-at.bofh.it> <tQbL4-4U-5@gated-at.bofh.it> <tQdMR-1yv-5@gated-at.bofh.it>
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On Thu, Jun 08, 2017 at 03:06:39PM -0700, subhra mazumdar wrote:
> 
> 
> On 06/08/2017 12:59 PM, Peter Zijlstra wrote:
> > On Thu, Jun 08, 2017 at 03:26:32PM -0400, Subhra Mazumdar wrote:
> > > Current select_idle_core tries to find a fully idle core and if it fails
> > > select_idle_cpu next returns any idle cpu in the llc domain. This is not optimal
> > > for architectures with many (more than 2) hyperthreads in a core. This patch
> > > changes select_idle_core to find the core with least number of busy
> > > hyperthreads and return an idle cpu in that core.
> > Yeah, I think not. That makes select_idle_siblings _vastly_ more
> > expensive.
> I am not sure if the cost will increase vastly. Firstly I removed the
> select_idle_cpu for archs that have SMT.

But you still do an unconditional scan of the full cache domain, that
alone is too expensive.

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[RFC PATCH] sched: select_idle_core should select least utilized core Subhra Mazumdar <subhra.mazumdar@oracle.com> - 2017-06-08 21:30 +0200
  Re: [RFC PATCH] sched: select_idle_core should select least utilized  core Peter Zijlstra <peterz@infradead.org> - 2017-06-08 22:00 +0200
    Re: [RFC PATCH] sched: select_idle_core should select least utilized  core subhra mazumdar <subhra.mazumdar@oracle.com> - 2017-06-09 00:10 +0200
      Re: [RFC PATCH] sched: select_idle_core should select least utilized  core Peter Zijlstra <peterz@infradead.org> - 2017-06-09 10:00 +0200

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