From owner-freebsd-current@FreeBSD.ORG Mon Aug 20 10:00:04 2012 Return-Path: Delivered-To: current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 0494D1065670; Mon, 20 Aug 2012 10:00:03 +0000 (UTC) (envelope-from mavbsd@gmail.com) Received: from mail-ey0-f182.google.com (mail-ey0-f182.google.com [209.85.215.182]) by mx1.freebsd.org (Postfix) with ESMTP id F208A8FC0C; Mon, 20 Aug 2012 10:00:02 +0000 (UTC) Received: by eaak11 with SMTP id k11so2037055eaa.13 for ; Mon, 20 Aug 2012 03:00:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=sender:message-id:date:from:user-agent:mime-version:to:cc:subject :references:in-reply-to:content-type:content-transfer-encoding; bh=uTpxsM9V4AZtucAoVNTw1DN/PP/hvRynPt2UYNtq6Yo=; b=p6UiSfb8LG/+QHkjbeaKwqy2M9pvNcCS+hHn44GeSpogUR54Bh6iDKFyM2RjFAVkRl xI2I1vqKN3pHUqt9uV64K9FNmddyeKwtS35JjsYMhJUetIFLLyK0hmetccAus9WfmruV urHvk5vyCCd2Bv67+D0rJ7kQJT2O582MT39khBg7J+3Sku4OMTnbnRMOLDYimpb1zOaK C1qYw/ixVJfyzbNGxo8M4uPNMtrjCwA9c1COfRh+c4uOgZF9BE5WEEp+32eZrvcRY9ms pnS9eEEeiNkpVfXNQ1bP8pNTE3kacn3JLBwTVRW44rSCghLpG/bHqcyiWTOdbr2hCfPb m0Uw== Received: by 10.14.1.9 with SMTP id 9mr7998146eec.9.1345456801915; Mon, 20 Aug 2012 03:00:01 -0700 (PDT) Received: from mavbook.mavhome.dp.ua ([91.198.175.1]) by mx.google.com with ESMTPS id 9sm40398353eei.12.2012.08.20.03.00.00 (version=TLSv1/SSLv3 cipher=OTHER); Mon, 20 Aug 2012 03:00:01 -0700 (PDT) Sender: Alexander Motin Message-ID: <50320A9E.5070303@FreeBSD.org> Date: Mon, 20 Aug 2012 12:59:58 +0300 From: Alexander Motin User-Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:13.0) Gecko/20120628 Thunderbird/13.0.1 MIME-Version: 1.0 To: Doug Barton References: <157941699.20120815004542@serebryakov.spb.ru> <502AE8B5.9090106@FreeBSD.org> <502B775D.7000101@FreeBSD.org> <5031F636.1020405@FreeBSD.org> In-Reply-To: <5031F636.1020405@FreeBSD.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Adrian Chadd , lev@freebsd.org, current@freebsd.org Subject: Re: CURRENT as gateway on not-so-fast hardware: where is a bottlneck? X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 20 Aug 2012 10:00:04 -0000 On 20.08.2012 11:32, Doug Barton wrote: > On 08/15/2012 03:18, Alexander Motin wrote: >> On 15.08.2012 03:09, Doug Barton wrote: >>> On 08/14/2012 12:20 PM, Adrian Chadd wrote: >>>> Would you be willing to compile a kernel with KTR so you can capture >>>> some KTR scheduler dumps? >>>> >>>> That way the scheduler peeps can feed this into schedgraph.py (and you >>>> can too!) to figure out what's going on. >>>> >>>> Maybe things aren't being scheduled correctly and the added latency is >>>> killing performance? >>> >>> You might also try switching to SCHED_ULE to see if it helps. >>> >>> Although, in the last few months as mav has been converging the 2 I've >>> started to see the same problems I saw on my desktop systems previously >>> re-appear even using ULE. For example, if I'm watching an AVI with VLC >>> and start doing anything that generates a lot of interrupts (like moving >>> large quantities of data from one disk to another) the video and sound >>> start to skip. Also, various other desktop features (like menus, window >>> switching, etc.) start to take measurable time to happen, sometimes >>> seconds. >>> >>> ... and lest you think this is just a desktop problem, I've seen the >>> same scenario on 8.x systems used as web servers. With ULE they were >>> frequently getting into peak load situations that created what I called >>> "mini thundering herd" problems where they could never quite get caught >>> up. Whereas switching to 4BSD the same servers got into high-load >>> situations less often, and they recovered on their own in minutes. >> >> It is quite pointless to speculate without real info like mentioned >> above KTR_SCHED traces. > > I'm sorry, you're quite wrong about that. In the cases I mentioned, and > in about 2 out of 3 of the cases where users reported problems and I > suggested that they try 4BSD, the results were clear. This obviously > points out that there is a serious problem with ULE, and if I were the > one who was responsible for that code I would be looking at ways of > helping users figure out where the problems are. But that's just me. I am not telling anything bad about 4BSD. Choice is provided because they are indeed different and none is perfect. 4BSD also has problems. What I would like to say is that if we want to improve situation, we need more detailed info then just verbal description. I am not telling that ULE is perfect. I went there because I've seen problems, and I am still fixing some pieces. I am just trying to explain described behavior from the point of my knowledge about it, hoping that it may help somebody to set up some new experiments or try some tuning/fixing. -- Alexander Motin