Messages in this thread | | | Subject | Re: [PATCH v2] futex: lower the lock contention on the HB lock during wake up | From | Mike Galbraith <> | Date | Sun, 21 Jun 2015 06:35:44 +0200 |
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On Wed, 2015-06-17 at 16:28 +0200, Sebastian Andrzej Siewior wrote: > On 06/17/2015 04:17 PM, Mike Galbraith wrote: > > On Wed, 2015-06-17 at 10:33 +0200, Sebastian Andrzej Siewior wrote: > >> wake_futex_pi() wakes the task before releasing the hash bucket lock > >> (HB). The first thing the woken up task usually does is to acquire the > >> lock which requires the HB lock. On SMP Systems this leads to blocking > >> on the HB lock which is released by the owner shortly after. > >> This patch rearranges the unlock path by first releasing the HB lock and > >> then waking up the task. > >> > >> [bigeasy: redo ontop of lockless wake-queues] > >> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> > >> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> > > > > 4.1-rc8-rt4 contains this via 4.0-rt4, and seems fine on my 64 core > > DL980. I ran a few iterations of futextests and stockfish, then mixed > > two loops of futextest at different rt prios, with stockfish also rt, > > and ltplight as tossed in as... crack filler. Box is still doing that, > > is way too busy, but not griping about it. > > There are two patches mostly doing the same thing. The patch posted > here is a redo ontop of "lockless wake-queues". It does hb-unlock, > wakeup, de-boost. The patch merged into -RT is the original approach > not using "lockless wake-queues" and performing wakeup, hb-unlock, > de-boost. > > I plan to get into -RT the final solution once it hits upstream.
I plugged patch1 and tip version into rt and beat it, seems solid.
Converting the rest of rtmutex.c to use wake queues with ->save_state to select wake function went less well. Kernel does a good impersonation of a working kernel until I beat it up, then it loses wakeups. Hohum, so much for yet another early morning tinker session.
-Mike
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