From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1422634AbWBAPby (ORCPT ); Wed, 1 Feb 2006 10:31:54 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1422633AbWBAPby (ORCPT ); Wed, 1 Feb 2006 10:31:54 -0500 Received: from smtp204.mail.sc5.yahoo.com ([216.136.130.127]:36742 "HELO smtp204.mail.sc5.yahoo.com") by vger.kernel.org with SMTP id S1422632AbWBAPbw (ORCPT ); Wed, 1 Feb 2006 10:31:52 -0500 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com.au; h=Received:Message-ID:Date:From:User-Agent:X-Accept-Language:MIME-Version:To:CC:Subject:References:In-Reply-To:Content-Type:Content-Transfer-Encoding; b=dzV9sPCFp96qseO9f8Oav9y+M7BRrcsbgKwJ7AbiovpxR+LSWzBUzwk1QE7ArxmHyiVltuxxsFFWo1vy0wO6mWI7wdtCYcBGE9nTkVWfFc38JPRFN/h4Zo4+LtMB/hc7Ql5u3MDbNJXQaLS6gIMtPqbYKY8tlqZvgo1TYuw4rkU= ; Message-ID: <43E0D464.2020509@yahoo.com.au> Date: Thu, 02 Feb 2006 02:31:48 +1100 From: Nick Piggin User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.12) Gecko/20051007 Debian/1.7.12-1 X-Accept-Language: en MIME-Version: 1.0 To: Ingo Molnar CC: Steven Rostedt , Peter Williams , Thomas Gleixner , Andrew Morton , LKML Subject: Re: [PATCH] Avoid moving tasks when a schedule can be made. References: <1138797874.7088.44.camel@localhost.localdomain> <43E0B24E.8080508@yahoo.com.au> <43E0B342.6090700@yahoo.com.au> <20060201132054.GA31156@elte.hu> <43E0BBEC.3020209@yahoo.com.au> <43E0BDA3.8040003@yahoo.com.au> <20060201141248.GA6277@elte.hu> <43E0C4CF.8090501@yahoo.com.au> <20060201143727.GA9915@elte.hu> <43E0CBBC.2000002@yahoo.com.au> <20060201151137.GA14794@elte.hu> In-Reply-To: <20060201151137.GA14794@elte.hu> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Ingo Molnar wrote: > * Nick Piggin wrote: >>If it were generated by some real workload that cares, then I would care. > > > well, you might not care, but i do. It's up to you what you care about, > but right now the scheduler policy is that we do care about latencies. > Yes, it's obviously all subject to common sense, and if something > triggers in a rare and extreme workload then any change related to it > has a _much_ higher barrier of acceptance than a common codepath. But > your blanket dismissal of this whole subject based on the rarity of the > workload is just plain wrong. > No, if you read what I'd been saying, I'm not dismissing the whole subject based on the workload. I'm saying that there is no point to include such a "fix" based on the numbers given by this workload (if there is a more meaningful one, then sure). Especially not while there are sources of equivalent latency. It is really simple: I can find a code path in the kernel, and work out how to exploit it by increasing resource loading until it goes bang (another example, tasklist_lock). This is not really a justification for trying to "fix" it. Unless somewhere there was an agreement that 1.5ms interrupt latency was a bug, full stop. > >>>to argue that 'you can get the same by using rwsems so why should we >>>bother' is pretty lame: rwsems are rare and arguably broken in >>>behavior, and i'd not say the same about the scheduler (just yet :-). >> >>I don't think it is lame at all. They're fairly important in use in >>mmap_sem that I know of. And I have seen workloads where the up_write >>path gets really expensive (arguably more relevant ones than >>hackbench). > > > they are broken e.g. in that they are mass-waking all the readers with > interrupts disabled. At a minimum rwsems should be declared irq-unsafe > (like mutexes), as all the substantial uses are in process-context > codepaths anyway. I'll revisit rwsems once the current mutex work is > done. > That would be great. Actually I have some patches that move the actual waking of the tasks out from underneath the lock too which gave some scalability benefits (and I'd imagine far less interrupt-off time, so let me know when you start work on rwsems). But there are still places where interrupts can be held off for indefinite periods. I don't see why the scheduler lock is suddenly important - I could have told you years ago what would happen if you trigger the load balancer with enough tasks. -- SUSE Labs, Novell Inc. Send instant messages to your online friends http://au.messenger.yahoo.com