From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michael Riepe Subject: ptrace performance (was: [Bug #12208] uml is very slow on 2.6.28 host) Date: Sat, 21 Mar 2009 15:44:17 +0100 Message-ID: <49C4FD41.4030504@googlemail.com> References: <9nR7rAsBwYG.A.iEG.fOCvJB@chimera> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=googlemail.com; s=gamma; h=domainkey-signature:received:received:message-id:date:from :user-agent:x-accept-language:mime-version:to:cc:subject:references :in-reply-to:x-enigmail-version:content-type :content-transfer-encoding; bh=NEADi6ZStyhNTK9WR4x/4tvHxKK/2bbG84n6e4KAS4g=; b=i09ok1LSTL8pmHZI4NqbD9rUq1WBAhincwo62Bnmd4HleNBVhrsmhx1k6K0s9XznJ9 9Yu7K+hnBhtzIJDNnvL+wSp6vAxzn4Dq6RHn0g/yVStCtuj5/gx8ionBb13ZOTOjOSy2 Y4t2lc4pitNQx0Kvd6/yCHxPIp1UTvpnmFj7o= In-Reply-To: Sender: kernel-testers-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" To: "Rafael J. Wysocki" Cc: Linux Kernel Mailing List , Kernel Testers List , Miklos Szeredi Disclaimer: I'm not using UML, but these problems may be related. > Bug-Entry : http://bugzilla.kernel.org/show_bug.cgi?id=12208 > Subject : uml is very slow on 2.6.28 host > Submitter : Miklos Szeredi > Date : 2008-12-12 9:35 (93 days old) > References : http://marc.info/?l=linux-kernel&m=122907463518593&w=4 The other day I noticed a dramatic ptrace slowdown between 2.6.27 and 2.6.28.x (verified with 2.6.28.8). In particular, a command like dd if=/dev/zero of=/dev/null bs=1024k count=1024 will normally report a throughput in the GB/s range. On 2.6.27, this is also true if you run strace -o /dev/null
which is only a little slower. But if I do the same on 2.6.28.x, I get a throughput of about 100 MB/s or less, i.e. less than 10%. I tried the commands on three different machines (an Athlon64 3000+, a Core Duo T2400 and an Atom 330), and they all behave similar. The more system calls a program uses, the worse the slowdown (try the dd command with bs=16k and count=65536, for example - but don't hold your breath). Interestingly, the CPUs are mostly idle while the command is executing on 2.6.28.x, but there is a high (system) load on 2.6.27. Therefore, I suspect that it's a scheduling or maybe timer problem that was introduced between 2.6.27 and 2.6.28. I haven't had the time to check the rc kernels yet; perhaps someone else can run a quick check to verify that it's gone in the latest 2.6.29-rc. -- Michael "Tired" Riepe X-Tired: Each morning I get up I die a little