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(). _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
