From owner-freebsd-current@FreeBSD.ORG Mon May 18 17:31:19 2009 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 3F1821065670; Mon, 18 May 2009 17:31:19 +0000 (UTC) (envelope-from jhb@freebsd.org) Received: from cyrus.watson.org (cyrus.watson.org [65.122.17.42]) by mx1.freebsd.org (Postfix) with ESMTP id 0F0658FC2C; Mon, 18 May 2009 17:31:19 +0000 (UTC) (envelope-from jhb@freebsd.org) Received: from bigwig.baldwin.cx (66.111.2.69.static.nyinternet.net [66.111.2.69]) by cyrus.watson.org (Postfix) with ESMTPSA id B206546B23; Mon, 18 May 2009 13:31:18 -0400 (EDT) Received: from jhbbsd.hudson-trading.com (unknown [209.249.190.8]) by bigwig.baldwin.cx (Postfix) with ESMTPA id 6D4A48A026; Mon, 18 May 2009 13:31:17 -0400 (EDT) From: John Baldwin To: Attilio Rao Date: Mon, 18 May 2009 13:31:10 -0400 User-Agent: KMail/1.9.7 References: <08D7DC2A-68BE-47B6-8D5D-5DE6B48F87E5@wanderview.com> <200905181129.51526.jhb@freebsd.org> <3bbf2fe10905181012t4bde260bp31181e3ea7b03a42@mail.gmail.com> In-Reply-To: <3bbf2fe10905181012t4bde260bp31181e3ea7b03a42@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Message-Id: <200905181331.11174.jhb@freebsd.org> X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.0.1 (bigwig.baldwin.cx); Mon, 18 May 2009 13:31:17 -0400 (EDT) X-Virus-Scanned: clamav-milter 0.95 at bigwig.baldwin.cx X-Virus-Status: Clean X-Spam-Status: No, score=-2.5 required=4.2 tests=AWL,BAYES_00,RDNS_NONE autolearn=no version=3.2.5 X-Spam-Checker-Version: SpamAssassin 3.2.5 (2008-06-10) on bigwig.baldwin.cx Cc: Adam McDougall , freebsd-current@freebsd.org, Artem Belevich , Ben Kelly Subject: Re: [patch] zfs livelock and thread priorities 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, 18 May 2009 17:31:19 -0000 On Monday 18 May 2009 1:12:59 pm Attilio Rao wrote: > 2009/5/18 John Baldwin : > > On Saturday 16 May 2009 12:40:44 pm Ben Kelly wrote: > >> =C2=A0 =C2=A01) It changes the kproc(9) API by adding a kproc_create_p= riority() > >> function that allows you to set the priority of the newly created > >> thread. =C2=A0I'm not sure how people feel about this. > > > > Actually, I almost think we should just add a priority argument to each= of=20 the > > routines that creates a new kthread/kproc. =C2=A0Perhaps allow a priori= ty of 0=20 to > > let the thread run with the default priority. =C2=A0Hmm, it looks like = kthreads > > default to running with whatever thread0 runs at (PVM) which is probabl= y=20 not > > really ideal. =C2=A0Having an explicit priority for every kthread would= =20 probably > > be best. =C2=A0Most kthreads should probably be at PZERO by default I t= hink. >=20 > I'm not sure I agree here. > 1) Maybe I missed it (so please point me to the right one) but I > didn't see a deep analysis of what messed up with the priorities there Solaris makes certain assumptions about the relative priorities of ZFS thre= ads=20 and our ZFS doesn't set the priorities the same. I think specifically ther= e=20 are "cleaner" threads which have a higher priority on Solaris than other ZF= S=20 threads and Solaris depends on that to avoid deadlocks. > 2) I think this KPI can be dangerous and lead to problems. Priority is > something highly fragile. All the more reason to make developers _think_ about the priority of each=20 kthread they create. Right now all these threads start out with a priority= =20 of PVM since that is what thread0 runs at. Does that sound right to you? = Do=20 you think many folks realize that? It sounds very bogus to me. I think=20 forcing people to pick a sensible priority for each thread is far better th= an=20 the complete lack of thought that often happens now. =2D-=20 John Baldwin