From owner-svn-src-head@freebsd.org Wed Nov 29 18:45:00 2017 Return-Path: Delivered-To: svn-src-head@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 37EACE65817; Wed, 29 Nov 2017 18:45:00 +0000 (UTC) (envelope-from hps@selasky.org) Received: from mail.turbocat.net (turbocat.net [88.99.82.50]) (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 C13D8803DE; Wed, 29 Nov 2017 18:44:59 +0000 (UTC) (envelope-from hps@selasky.org) Received: from hps2016.home.selasky.org (unknown [62.141.128.70]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.turbocat.net (Postfix) with ESMTPSA id F292F2602F2; Wed, 29 Nov 2017 19:44:55 +0100 (CET) Subject: Re: svn commit: r326218 - head/sys/kern To: Justin Hibbits , Konstantin Belousov Cc: John Baldwin , Nathan Whitehorn , src-committers , "svn-src-all@freebsd.org" , "svn-src-head@freebsd.org" , Konstantin Belousov , "O. Hartmann" , KrishnamRaju ErapaRaju References: <201711252341.vAPNf5Qx001464@repo.freebsd.org> <14322447.103fKFTi3y@ralph.baldwin.cx> <3fc45d5f-22b9-0562-278b-c515e36f48e7@freebsd.org> <14058479.lc6xlYgyBM@ralph.baldwin.cx> <2e752d6a-d34a-dde0-acea-fdbf8bebea51@selasky.org> <20171129161356.GA2272@kib.kiev.ua> From: Hans Petter Selasky Message-ID: <0baa25c3-f235-78c5-5c72-9eab5dab89c6@selasky.org> Date: Wed, 29 Nov 2017 19:42:10 +0100 User-Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Mailman-Approved-At: Wed, 29 Nov 2017 19:00:58 +0000 X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.25 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 29 Nov 2017 18:45:00 -0000 On 11/29/17 17:59, Justin Hibbits wrote: > On Wed, Nov 29, 2017 at 10:13 AM, Konstantin Belousov > wrote: >> On Wed, Nov 29, 2017 at 04:33:50PM +0100, Hans Petter Selasky wrote: >>> Hi Nathan, >>> >>> The chunk below causes sched_pin() to stop working and should be removed >>> from your commit ??!! >>> >>> It probably explains the hangs seen recently reported by various brave >>> people running 12-current :-) >>> >>> Specifically I see threads migrating between CPUs when td->td_pinned > 0 >>> using the LinuxKPI RCU API, which in turn leads to a hang when trying to >>> synchronize RCU. >>> >>> --HPS >>> >>> diff --git a/sys/kern/sched_ule.c b/sys/kern/sched_ule.c >>> index 5c8bae5afa1..bd4b505f6c3 100644 >>> --- a/sys/kern/sched_ule.c >>> +++ b/sys/kern/sched_ule.c >>> @@ -2453,7 +2453,7 @@ sched_add(struct thread *td, int flags) >>> * Pick the destination cpu and if it isn't ours transfer to the >>> * target cpu. >>> */ >>> - td_get_sched(td)->ts_cpu = curcpu; /* Pick something valid to >>> start */ >>> +// td_get_sched(td)->ts_cpu = curcpu; /* Pick something valid to >>> start */ >>> cpu = sched_pickcpu(td, flags); >>> tdq = sched_setcpu(td, cpu, flags); >>> tdq_add(tdq, td, flags); >> >> To clarify. It seems that this change breaks sched_bind(). >> >> It might be that LinuxKPI does use sched_pin() in somewhat questionable >> way. Namely, the code puts the thread off the CPU (e.g. by taking a >> lock). Then, is it guaranteed that the pinned thread returns to the same >> cpu after sched_add() ? >> >> I think that the second behaviour is not guaranteed, but it might >> happens by the way the things are arranged. If guaranteed, then the >> sched_pin() breakage is same as for sched_bind(). >> > > I see the same breakage on PowerPC with the dtsec(4) driver, which > pins interrupts to CPUs, now causing interrupts to migrate to cores > without the matching portal mapping. > > - Justin Hi Nathan, Looking at your patch I think what you wanted to do is something like shown below. I'm not sure if sched_setup() is run early enough to catch all created threads in the registered eventhandler hook. I'll leave the final solution and analysis up to you. --HPS > diff --git a/sys/kern/sched_ule.c b/sys/kern/sched_ule.c > index 5c8bae5afa1..42ccf58ea0c 100644 > --- a/sys/kern/sched_ule.c > +++ b/sys/kern/sched_ule.c > @@ -1387,6 +1387,13 @@ sched_setup_smp(void) > } > #endif > > +static void > +sched_thread_ctor(void *arg __unused, struct thread *td) > +{ > + /* Pick a valid initial CPU number */ > + td_get_sched(td)->ts_cpu = curcpu; > +} > + > /* > * Setup the thread queues and initialize the topology based on MD > * information. > @@ -1396,6 +1403,9 @@ sched_setup(void *dummy) > { > struct tdq *tdq; > > + (void) EVENTHANDLER_REGISTER(thread_ctor, > + sched_thread_ctor, NULL, EVENTHANDLER_PRI_ANY); > + > tdq = TDQ_SELF(); > #ifdef SMP > sched_setup_smp(); > @@ -2453,7 +2463,6 @@ sched_add(struct thread *td, int flags) > * Pick the destination cpu and if it isn't ours transfer to the > * target cpu. > */ > - td_get_sched(td)->ts_cpu = curcpu; /* Pick something valid to start */ > cpu = sched_pickcpu(td, flags); > tdq = sched_setcpu(td, cpu, flags); > tdq_add(tdq, td, flags);