Messages in this thread | | | From | Andrei Vagin <> | Date | Wed, 26 Apr 2023 11:52:49 -0700 | Subject | Re: [PATCH 3/6] sched: add a few helpers to wake up tasks on the current cpu |
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On Wed, Apr 26, 2023 at 7:43 AM Bernd Schubert <bschubert@ddn.com> wrote: > > > Add complete_on_current_cpu, wake_up_poll_on_current_cpu helpers to wake > > up tasks on the current CPU. > > > These two helpers are useful when the task needs to make a synchronous context > > switch to another task. In this context, synchronous means it wakes up the > > target task and falls asleep right after that. > > > One example of such workloads is seccomp user notifies. This mechanism allows > > the supervisor process handles system calls on behalf of a target process. > > While the supervisor is handling an intercepted system call, the target process > > will be blocked in the kernel, waiting for a response to come back. > > > On-CPU context switches are much faster than regular ones. > > > Signed-off-by: Andrei Vagin <avagin@google.com> > > Avoiding cpu switches is very desirable for fuse, I'm working on fuse over uring > with per core queues. In my current branch and running a single threaded bonnie++ > I get about 9000 creates/s when I bind the process to a core, about 7000 creates/s > when I set SCHED_IDLE for the ring threads and back to 9000 with SCHED_IDLE and > disabling cpu migration in fs/fuse/dev.c request_wait_answer() before going into > the waitq and enabling it back after waking up. > > I had reported this a few weeks back > https://lore.kernel.org/lkml/d0ed1dbd-1b7e-bf98-65c0-7f61dd1a3228@ddn.com/ > and had been pointed to your and Prateeks patch series. I'm now going > through these series. Interesting part is that a few weeks I didn't need > SCHED_IDLE, just disabling/enabling migration before/after waking up was > enough. > > [...] > > > EXPORT_SYMBOL(swake_up_one); > > diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c > > index 133b74730738..47803a0b8d5d 100644 > > --- a/kernel/sched/wait.c > > +++ b/kernel/sched/wait.c > > @@ -161,6 +161,11 @@ int __wake_up(struct wait_queue_head *wq_head, unsigned int mode, > > } > > EXPORT_SYMBOL(__wake_up); > > > +void __wake_up_on_current_cpu(struct wait_queue_head *wq_head, unsigned int mode, void *key) > > +{ > > + __wake_up_common_lock(wq_head, mode, 1, WF_CURRENT_CPU, key); > > +} > > I'm about to test this instead of migrate_disable/migrate_enable, but the symbol needs > to be exported - any objection to do that right from the beginning in your patch?
I think EXPORT_SYMBOL_GPL should not trigger any objections and it covers your case, doesn't it?
Thanks, Andrei
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