Messages in this thread | | | Subject | Re: [patch v2 1/2] sched: check for prev_cpu == this_cpu before calling wake_affine() | From | Mike Galbraith <> | Date | Fri, 02 Apr 2010 21:43:27 +0200 |
| |
On Fri, 2010-04-02 at 10:05 -0700, Suresh Siddha wrote: > On Thu, 2010-04-01 at 23:20 -0700, Mike Galbraith wrote: > > Yes, if task A and task B are more or less unrelated, you'd want them to > > stay in separate domains, you'd not want some random event to pull. The > > other side of the coin is tasks which fork off partners that they will > > talk to at high frequency. They land just as far away, and desperately > > need to move into a shared cache domain. There's currently no > > discriminator, so while always asking wake_affine() may reduce the risk > > of moving a task with a large footprint, it also increases the risk of > > leaving buddies jabbering cross cache. > > Mike, Apart from this small tweak that you added in wake_up() path there > is no extra logic that keeps buddies together for long.
The wakeup logic is the only thing that keeps buddies together.
> As I was saying, > fork/exec balance starts apart and in the partial loaded case (i.e., > when # of running tasks <= # of sockets or # of total cores) the default > load balancer policy also tries to distribute the load equally among > sockets/cores (for peak cache/memory controller bw etc). While the > wakeup() may keep the buddies on SMT siblings, next load balancing event > will move them far away. If we need to keep buddies together we need > more changes than this small tweak.
We very definitely need to keep buddies cache affine. Yes, maybe some additional logic is needed, as there is a conflict between load types. A kbuild spreading to the four winds is fine, while netperf jabbering cross cache is horrible.
> > Do you have a compute load bouncing painfully which this patch cures? > > > > I have no strong objections, and the result is certainly easier on the > > eye. If I were making the decision, I'd want to see some numbers. > > All I saw in the changelog when you added this new tweak was: > > commit 8b911acdf08477c059d1c36c21113ab1696c612b > Author: Mike Galbraith <efault@gmx.de> > Date: Thu Mar 11 17:17:16 2010 +0100 > > sched: Fix select_idle_sibling() > > Don't bother with selection when the current cpu is idle. .... > > Is it me or you who need to provide the data for justification for your > new tweak that changes the current behavior ;) > > I will run some workloads aswell!
Whoa. It was a simple question, no need to get defensive. You need not provide anything. Forget I even asked, it's not my decision.
-Mike
| |