Date: Wed, 29 Nov 2017 10:59:34 -0600 From: Justin Hibbits <jrh29@alumni.cwru.edu> To: Konstantin Belousov <kostikbel@gmail.com> Cc: Hans Petter Selasky <hps@selasky.org>, John Baldwin <jhb@freebsd.org>, Nathan Whitehorn <nwhitehorn@freebsd.org>, src-committers <src-committers@freebsd.org>, "svn-src-all@freebsd.org" <svn-src-all@freebsd.org>, "svn-src-head@freebsd.org" <svn-src-head@freebsd.org>, Konstantin Belousov <kib@freebsd.org>, "O. Hartmann" <ohartmann@walstatt.org>, KrishnamRaju ErapaRaju <Krishna2@chelsio.com> Subject: Re: svn commit: r326218 - head/sys/kern Message-ID: <CAHSQbTAfQcudcVRUGR=wwm9hvbgvhaFuTVjA8D15C%2B8fRfN=hw@mail.gmail.com> In-Reply-To: <20171129161356.GA2272@kib.kiev.ua> 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>
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On Wed, Nov 29, 2017 at 10:13 AM, Konstantin Belousov <kostikbel@gmail.com> 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
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