linux-kernel - Re: Slowdown due to threads bouncing between HT cores

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Message-ID: <20141004092205.GA12973@localhost>
Date:	Sat, 4 Oct 2014 11:22:05 +0200
From:	Marc Burkhardt <marc@...nowledge.org>
To:	"Steinar H. Gunderson" <sgunderson@...foot.com>
Cc:	Marc Burkhardt <marc@...nowledge.org>, linux-kernel@...r.kernel.org
Subject: Re: Slowdown due to threads bouncing between HT cores

* Steinar H. Gunderson <sgunderson@...foot.com> [2014-10-03 23:14:17 +0200]:

> On Fri, Oct 03, 2014 at 11:11:52PM +0200, Marc Burkhardt wrote:
> > As I understand your mail, you problem is quite similar, isn't it?
> 
> I guess it depends on how often your process migrates. If it happens, like,
> every second, it's not a big problem (and probably is expected).
> If it happens all the time, it might be; it depends a bit on a number of
> factors.

Hi Steinar,

you say the behavior is probably expected, but I still don't get the point why
this could be normal or even wanted. There's a cost for migrating the process to
another CPU. In case my machine has 4 cores, 3 of them 'idle' and that 1 running
process that keeps being migrated ... where's the benefit of migrating it?

Do you have any source/docs where I could read about this?

Thanks,
Marc

> 
> /* Steinar */
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Marc Burkhardt
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