Messages in this thread | | | Date | Thu, 5 Mar 2020 19:51:36 +0100 | From | Peter Zijlstra <> | Subject | Re: 'simple' futex interface [Was: [PATCH v3 1/4] futex: Implement mechanism to wait on any of several futexes] |
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On Thu, Mar 05, 2020 at 01:14:17PM -0300, André Almeida wrote:
> > sys_futex_wait(void *uaddr, u64 val, unsigned long flags, ktime_t *timo); > > struct futex_wait { > > void *uaddr; > > u64 val; > > u64 flags; > > }; > > sys_futex_waitv(struct futex_wait *waiters, unsigned int nr_waiters, > > u64 flags, ktime_t *timo); > > sys_futex_wake(void *uaddr, unsigned int nr, u64 flags); > > sys_futex_cmp_requeue(void *uaddr1, void *uaddr2, unsigned int nr_wake, > > unsigned int nr_requeue, u64 cmpval, unsigned long flags); > > > > And that makes 7 arguments for cmp_requeue, which can't be. Maybe we if > > combine nr_wake and nr_requeue in one as 2 u16... ? > > > > And then we need to go detector if the platform supports it or not.. > > > > Thanks everyone for the feedback around our mechanism. Are the > performance benefits of implementing a syscall to wait on a single futex > significant enough to maintain it instead of just using > `sys_futex_waitv()` with `nr_waiters = 1`? If we join both cases in a > single interface, we may even add a new member for NUMA hint in `struct > futex_wait`.
My consideration was that avoiding the get_user/copy_from_user might become measurable on !PTI systems with SMAP.
But someone would have to build it and measure it before we can be sure of course.
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