LKML Archive on lore.kernel.org
 help / color / Atom feed
From: Mel Gorman <mgorman@suse.de>
To: Preeti Murthy <preeti.lkml@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Thomas Hellstrom <thellstrom@vmware.com>,
	Rik van Riel <riel@redhat.com>,
	linux-kernel@vger.kernel.org,
	Preeti U Murthy <preeti@linux.vnet.ibm.com>
Subject: Re: [PATCH] sched: Calculate effective load even if local weight is 0
Date: Fri, 17 Jan 2014 14:56:27 +0000
Message-ID: <20140117145627.GY4963@suse.de> (raw)
In-Reply-To: <CAM4v1pNQsoJxgC9Kwe+ca=hSbDYr3huNrchzqWEvs26AfypmSw@mail.gmail.com>

On Mon, Jan 13, 2014 at 01:22:40PM +0530, Preeti Murthy wrote:
> Hi,
> 
> On Mon, Jan 6, 2014 at 5:09 PM, Mel Gorman <mgorman@suse.de> wrote:
> > (Rik, you authored this patch so it should be sent from you and needs a
> > signed-off assuming people are ok with the changelog.)
> >
> > Thomas Hellstrom bisected a regression where erratic 3D performance is
> > experienced on virtual machines as measured by glxgears. It identified
> > commit 58d081b5 (sched/numa: Avoid overloading CPUs on a preferred NUMA
> > node) as the problem which had modified the behaviour of effective_load.
> >
> > Effective load calculates the difference to the system-wide load if a
> > scheduling entity was moved to another CPU. The task group is not heavier
> > as a result of the move but overall system load can increase/decrease as a
> > result of the change. Commit 58d081b5 (sched/numa: Avoid overloading CPUs
> > on a preferred NUMA node) changed effective_load to make it suitable for
> > calculating if a particular NUMA node was compute overloaded. To reduce
> > the cost of the function, it assumed that a current sched entity weight
> > of 0 was uninteresting but that is not the case.
> >
> > wake_affine uses a weight of 0 for sync wakeups on the grounds that it
> > is assuming the waking task will sleep and not contribute to load in the
> > near future. In this case, we still want to calculate the effective load
> > of the sched entity hierarchy. As effective_load is no longer used by
> 
> Would it be worth mentioning that besides sync wakeups, wake_affine() uses a
> weight of 0 for the sched entity, for effective load calculation on
> the prev_cpu as well?
> This is so as to find the effect of  moving this task away from the
> prev_cpu. Here
> too we are interested in calculating the effective load of the root
> task group of this
> sched entity on the prev_cpu and the below restored check will be relevant.
> 
> Without the below check the difference in the loads of the wake affine
> CPU and the
> prev_cpu can get messed up.
> 

I was too slow getting to this mail unfortunately. The patch is already
merged upstream with the changelog as-is.

-- 
Mel Gorman
SUSE Labs

      reply index

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-01-06 11:39 Mel Gorman
2014-01-06 12:34 ` Peter Zijlstra
2014-01-06 13:09   ` Mel Gorman
2014-01-06 12:35 ` Peter Zijlstra
2014-01-06 14:00   ` Rik van Riel
2014-01-12 18:42 ` [tip:sched/urgent] " tip-bot for Rik van Riel
2014-01-13  7:52 ` [PATCH] " Preeti Murthy
2014-01-17 14:56   ` Mel Gorman [this message]

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20140117145627.GY4963@suse.de \
    --to=mgorman@suse.de \
    --cc=linux-kernel@vger.kernel.org \
    --cc=peterz@infradead.org \
    --cc=preeti.lkml@gmail.com \
    --cc=preeti@linux.vnet.ibm.com \
    --cc=riel@redhat.com \
    --cc=thellstrom@vmware.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

LKML Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
	git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
	git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
	git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
	git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
	git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
	git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
	git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git
	git clone --mirror https://lore.kernel.org/lkml/8 lkml/git/8.git
	git clone --mirror https://lore.kernel.org/lkml/9 lkml/git/9.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
		linux-kernel@vger.kernel.org
	public-inbox-index lkml

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git