From owner-svn-src-all@FreeBSD.ORG Tue Jan 20 23:46:49 2015 Return-Path: Delivered-To: svn-src-all@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id D33B4E0; Tue, 20 Jan 2015 23:46:48 +0000 (UTC) Received: from mail.ignoranthack.me (ignoranthack.me [199.102.79.106]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 980D4F44; Tue, 20 Jan 2015 23:46:48 +0000 (UTC) Received: from [192.168.200.212] (unknown [50.136.155.142]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) (Authenticated sender: sbruno@ignoranthack.me) by mail.ignoranthack.me (Postfix) with ESMTPSA id 54547192A3B; Tue, 20 Jan 2015 23:46:47 +0000 (UTC) Message-ID: <54BEE8E6.3080009@ignoranthack.me> Date: Tue, 20 Jan 2015 15:46:46 -0800 From: Sean Bruno Reply-To: sbruno@freebsd.org User-Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: "K. Macy" Subject: Re: svn commit: r277213 - in head: share/man/man9 sys/kern sys/ofed/include/linux sys/sys References: <201501151532.t0FFWV2Y037455@svn.freebsd.org> <54BDD9E1.6090505@selasky.org> <20150120075126.GA42409@kib.kiev.ua> <20150120211137.GY15484@FreeBSD.org> <54BED6FB.8060401@selasky.org> <54BEE62D.2060703@ignoranthack.me> In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: Hans Petter Selasky , Adrian Chadd , "src-committers@freebsd.org" , Jason Wolfe , "svn-src-all@freebsd.org" , "svn-src-head@freebsd.org" , Gleb Smirnoff , Konstantin Belousov X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 20 Jan 2015 23:46:49 -0000 -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 On 01/20/15 15:40, K. Macy wrote: > I think you're working around driver locking bugs by crippling the > callout code. > > -K > We had zero evidence of this. What leads you down that path? I'm totally open to being wrong, e.g. "yeah, you slowed down things so that you don't hit a race condition" sean > On Tue, Jan 20, 2015 at 3:35 PM, Sean Bruno > wrote: On 01/20/15 14:30, Hans Petter > Selasky wrote: >>>> On 01/20/15 22:11, Gleb Smirnoff wrote: >>>>> On Tue, Jan 20, 2015 at 09:51:26AM +0200, Konstantin >>>>> Belousov wrote: K> > Like stated in the manual page, >>>>> callout_reset_curcpu/on() does not work K> > with MPSAFE >>>>> callouts any more! K> I.e. you 'fixed' some undeterminate >>>>> bugs in callout migration by not K> doing migration at all >>>>> anymore. K> K> > K> > You need to use >>>>> callout_init_{mtx,rm,rw} and remove the custom locking K> > >>>>> inside the callback in the TCP stack to get it working like >>>>> before! K> K> No, you need to do this, if you think that >>>>> whole callout KPI must be K> rototiled. It is up to the >>>>> person who modifies the KPI, to ensure that K> existing >>>>> code is not broken. K> K> As I understand, currently we are >>>>> back to the one-cpu callouts. K> Do other people consider >>>>> this situation acceptable ? >>>>> >>>>> I think this isn't acceptable. The commit to a complex >>>>> subsystem lacked a review from persons involved in the >>>>> system before. The commit to subsystem broke consumers of >>>>> the subsystem and this was even done not accidentially, but >>>>> due to Hans not caring about it. >>>>> >>>>> As for me this is enough to request a backout, and let the >>>>> change back in only after proper review. >>>>> >>>> >>>> Hi Gleb, >>>> >>>> Backing out my callout API patch means we will for sure >>>> re-introduce an unknown callout spinlock hang, as noted to me >>>> by several people. What do you think about that? dram Maybe >>>> "Jason Wolfe" CC'ed can add to 10-stable w/o my patches: >>>> > > Jason picked up this patch for work and it resolved our > instability issues that had remained unsolved for quite some time > as reported to freebsd-net: > > https://lists.freebsd.org/pipermail/freebsd-net/2015-January/040895.html > > This had gone undiagnosed for some time (even with the gracious > help of jhb in offline emails, thanks btw!). > > There's some diagnostics in that email thread that may be of value > to you folks for determination of the validity of changing the > callout API or at least understanding why we were involved in > diagnostics. > > While I'd sure love to tune performance, the fact that our > machines were basically going out to lunch without these changes, > probably means that others were seeing it and didn't know what else > to do. As much as I enjoy a good "break out the pitch forks and > torches" email thread, this increased stability for us and is > allowing us to upgrade from freebsd8 to freebsd10. Bear this in > mind when you throw your voice in favor of reverting. > >>>> int callout_reset_sbt_on(struct callout *c, sbintime_t sbt, >>>> sbintime_t precision, void (*ftn)(void *), void *arg, int >>>> cpu, int flags) { sbintime_t to_sbt, pr; struct callout_cpu >>>> *cc; int cancelled, direct; >>>> >>>> + cpu = timeout_cpu; /* XXX test code XXX */ >>>> >>>> cancelled = 0; >>>> > > Jason or I would have to run this in production, which would be > problematic I fear. We never had a deterministic test case that > would exhibit the reported failure. We merely "tested in > production" and saw that panics ceased. We didn't note a dropoff > in our traffic either, perhaps we are not as efficient as others in > this corner case, but we were consistently seeing the spinlock > hangs after a day or so of traffic. > >>>> And see if he observes a callout spinlock hang or not on his >>>> test setup. The patch above should force all callouts to the >>>> same thread basically. Then we could maybe see if single >>>> threading the callouts has anything to do with solving the >>>> spinlock hang. >>>> >>>> The "rewritten" callout API still has all the features and >>>> capabilities the old one had, when used as described in "man >>>> 9 callout". >>>> >>>> At the present moment I'm not technically convinced a backout >>>> is correct. > > Neither am I, to be honest. Just based on *results*. > >>>> >>>> Gleb: I think we would see far better results with high >>>> speed internet links using TCP if we could extend the LRO >>>> (large receive offload) code to accumulate more than 64KBytes >>>> worth of data per call to the TCP stack instead of >>>> complaining about some callouts ending up on the same thread! >>>> Actually I have a patch for that. >>>> >>>> --HPS >>>> >>>> >>>> > >> _______________________________________________ >> svn-src-head@freebsd.org mailing list >> http://lists.freebsd.org/mailman/listinfo/svn-src-head To >> unsubscribe, send any mail to >> "svn-src-head-unsubscribe@freebsd.org" > > -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQF8BAEBCgBmBQJUvujmXxSAAAAAAC4AKGlzc3Vlci1mcHJAbm90YXRpb25zLm9w ZW5wZ3AuZmlmdGhob3JzZW1hbi5uZXRCQUFENDYzMkU3MTIxREU4RDIwOTk3REQx MjAxRUZDQTFFNzI3RTY0AAoJEBIB78oecn5kv2MH/1F15x/lgwWq5fE/cZ3n9HlV 9Nd7DU03coj9qUU6LH1eLPPuUn7yelCw8xxtb0qOTIDyrzNYe+HIaJi1GMHkV8Ve iKFuB1G9gcN/nQ5BdaAezOazEUcRY2msigMh5n/2X/UDRzLAGfhbDFbogpRy1TyI fqKzYDM8Mx9yZfCuc4/yBUVmxDcVn6NsuQ7CW745qXQcrELdJ8fjKfaYWbprCR7u xA3Iwiio9Bv0/8MvR9n3PZ8z3NjAKD1XxV5iAPI+ANc/5Rc60cSmtP0mQakqOoz6 8uucaus79KdykdNovh31ka0dp0JBCghZOsfNXP69TFfvSXyngMZqwZgqVLVcX3M= =0AV4 -----END PGP SIGNATURE-----