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From: Bill Davidsen <davidsen@tmr.com>
To: Olof Johansson <olof@lixom.net>
Cc: Willy Tarreau <w@1wt.eu>, Mike Galbraith <efault@gmx.de>,
	linux-kernel@vger.kernel.org,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Ingo Molnar <mingo@elte.hu>
Subject: Re: Scheduler(?) regression from 2.6.22 to 2.6.24 for short-lived threads
Date: Mon, 11 Feb 2008 16:45:12 -0500	[thread overview]
Message-ID: <47B0C1E8.2050809@tmr.com> (raw)
In-Reply-To: <20080210052941.GA4731@lixom.net>

Olof Johansson wrote:

>> However, I fail to understand the goal of the reproducer. Granted it shows
>> irregularities in the scheduler under such conditions, but what *real*
>> workload would spend its time sequentially creating then immediately killing
>> threads, never using more than 2 at a time ?
>>
>> If this could be turned into a DoS, I could understand, but here it looks
>> a bit pointless :-/
> 
> It seems generally unfortunate that it takes longer for a new thread to
> move over to the second cpu even when the first is busy with the original
> thread. I can certainly see cases where this causes suboptimal overall
> system behaviour.
> 
I think the moving to another CPU gets really dependent on the CPU type. 
On a P4+HT the caches are shared, and moving costs almost nothing for 
cache hits, while on CPUs which have other cache layouts the migration 
cost is higher. Obviously multi-core should be cheaper than 
multi-socket, by avoiding using the system memory bus, but it still can 
get ugly.

I have an IPC test around which showed that, it ran like hell on HT, and 
progressively worse as cache because less shared. I wonder why the 
latest git works so much better?

-- 
Bill Davidsen <davidsen@tmr.com>
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot

  parent reply	other threads:[~2008-02-11 21:44 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-09  0:04 Olof Johansson
2008-02-09  0:08 ` Ingo Molnar
2008-02-09  0:32   ` Olof Johansson
2008-02-09  7:58 ` Mike Galbraith
2008-02-09  8:03   ` Willy Tarreau
2008-02-09 10:58     ` Mike Galbraith
2008-02-09 11:40       ` Willy Tarreau
2008-02-09 13:37         ` Mike Galbraith
2008-02-09 16:19           ` Willy Tarreau
2008-02-09 17:33             ` Mike Galbraith
2008-02-10  5:29             ` Olof Johansson
2008-02-10  6:15               ` Willy Tarreau
2008-02-10  7:00                 ` Olof Johansson
2008-02-10  7:58                   ` Willy Tarreau
2008-02-11  8:15                   ` Mike Galbraith
2008-02-11 17:26                     ` Olof Johansson
2008-02-11 19:58                       ` Mike Galbraith
2008-02-11 20:31                         ` Olof Johansson
2008-02-12  9:23                           ` Mike Galbraith
2008-02-13  5:49                             ` Mike Galbraith
2008-02-11 21:45               ` Bill Davidsen [this message]
2008-02-12  4:30                 ` Mike Galbraith
     [not found] <fa.6N2dhyJ1cmBqiuFKgCaYfwduM+0@ifi.uio.no>
2008-02-09  1:49 ` Robert Hancock

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