Messages in this thread | | | Subject | Re: 20% performance drop on PostgreSQL 9.2 from kernel 3.5.3 to 3.6-rc5 on AMD chipsets - bisected | From | Suresh Siddha <> | Date | Tue, 25 Sep 2012 14:11:51 -0700 |
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On Mon, 2012-09-24 at 12:12 -0700, Linus Torvalds wrote: > On Mon, Sep 24, 2012 at 11:26 AM, Mike Galbraith <efault@gmx.de> wrote: > > > > Aside from the cache pollution I recall having been mentioned, on my > > E5620, cross core is a tbench win over affine, cross thread is not. > > Oh, I agree with trying to avoid HT threads, the resource contention > easily gets too bad. > > It's more a question of "if we have real cores with separate L1's but > shared L2's, go with those first, before we start distributing it out > to separate L2's".
There is one issue though. If the tasks continue to run in this state and the periodic balance notices an idle L2, it will force migrate (using active migration) one of the tasks to the idle L2. As the periodic balance tries to spread the load as far as possible to take maximum advantage of the available resources (and the perf advantage of this really depends on the workload, cache usage/memory bw, the upside of turbo etc).
But I am not sure if this was the reason why we chose to spread it out to separate L2's during wakeup.
Anyways, this is one of the places where the Paul Turner's task load average tracking patches will be useful. Depending on how long a task typically runs, we can probably even chose a SMT siblings or a separate L2 to run.
thanks, suresh
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