From: "Martin J. Bligh" <mbligh@aracnet.com>
To: Andrew Theurer <habanero@us.ibm.com>, Ingo Molnar <mingo@elte.hu>,
linux-kernel@vger.kernel.org
Cc: ricklind@us.ibm.com
Subject: Re: [patch] HT scheduler, sched-2.5.68-B2
Date: Wed, 23 Apr 2003 15:38:35 -0700 [thread overview]
Message-ID: <1574320000.1051137515@flay> (raw)
In-Reply-To: <1538380000.1051123399@flay>
>>> > - turn off the more agressive idle-steal variant. This could fix the
>>> > low-load regression reported by Martin J. Bligh.
>>>
>>> Yup, that fixed it (I tested just your first version with just that
>>> bit altered).
>>
>> Can we make this an arch specific option? I have a feeling the HT performance
>> on low loads will actually drop with this disabled.
Actually, what must be happening here is that we're agressively stealing
things on non-HT machines ... we should be able to easily prevent that.
Suppose we have 2 real cpus + HT ... A,B,C,D are the cpus, where A, B
are HT twins, and C,D are HT twins. A&B share runqueue X, and C&D share
runqueue Y
What I presume you're trying to do is when A and B are running 1 task
each, and C and D are not running anything, balance out so we have
one on A and one on C. If we define some "nr_active(rq)" concept to be
the number of tasks actually actively running on cpus, then if we we're
switching from nr_actives of 2/0 to 1/0.
However, we don't want to switch from 2/1 to 1/2 ... that's pointless.
Or 0/1 to 1/0 (which I think it's what's happening). But in the case
where we had (theoretically) 4 HT siblings per real cpu, we would want
to migrate 1/3 to 2/2.
The key is that we want to agressively steal when
nr_active(remote) - nr_active(idle) > 1 ... not > 0.
This will implicitly *never* happen on non HT machines, so it seems
like a nice algorithm ... ?
M.
next prev parent reply other threads:[~2003-04-23 22:36 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-04-23 16:23 [patch] HT scheduler, sched-2.5.68-B2 Ingo Molnar
2003-04-23 17:47 ` Martin J. Bligh
2003-04-23 17:53 ` Andrew Theurer
2003-04-23 18:43 ` Martin J. Bligh
2003-04-23 20:14 ` Andrew Theurer
2003-04-24 8:43 ` Rick Lindsley
2003-04-24 14:23 ` Andrew Theurer
2003-04-23 22:38 ` Martin J. Bligh [this message]
2003-04-24 21:29 ` Bill Davidsen
2003-04-24 22:39 ` Martin J. Bligh
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