From: David Laight <David.Laight@ACULAB.COM>
To: "'Peter Zijlstra'" <peterz@infradead.org>,
"André Almeida" <andrealmeid@collabora.com>
Cc: Florian Weimer <fweimer@redhat.com>,
"Pierre-Loup A. Griffais" <pgriffais@valvesoftware.com>,
Thomas Gleixner <tglx@linutronix.de>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"kernel@collabora.com" <kernel@collabora.com>,
"krisman@collabora.com" <krisman@collabora.com>,
"shuah@kernel.org" <shuah@kernel.org>,
"linux-kselftest@vger.kernel.org"
<linux-kselftest@vger.kernel.org>,
"rostedt@goodmis.org" <rostedt@goodmis.org>,
"ryao@gentoo.org" <ryao@gentoo.org>,
"dvhart@infradead.org" <dvhart@infradead.org>,
"mingo@redhat.com" <mingo@redhat.com>,
"z.figura12@gmail.com" <z.figura12@gmail.com>,
"steven@valvesoftware.com" <steven@valvesoftware.com>,
"steven@liquorix.net" <steven@liquorix.net>,
"malteskarupke@web.de" <malteskarupke@web.de>,
"carlos@redhat.com" <carlos@redhat.com>,
"adhemerval.zanella@linaro.org" <adhemerval.zanella@linaro.org>,
"libc-alpha@sourceware.org" <libc-alpha@sourceware.org>,
"linux-api@vger.kernel.org" <linux-api@vger.kernel.org>
Subject: RE: 'simple' futex interface [Was: [PATCH v3 1/4] futex: Implement mechanism to wait on any of several futexes]
Date: Fri, 6 Mar 2020 16:57:54 +0000 [thread overview]
Message-ID: <0271e473ddcf463bb030eb4cbecbe888@AcuMS.aculab.com> (raw)
In-Reply-To: <20200305185136.GB3348@worktop.programming.kicks-ass.net>
From: Peter Zijlstra
> Sent: 05 March 2020 18:52
+> 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.
An extra copy_from_user is likely to be noticable.
It certainly makes recvmsg() slower than recv().
Especially if the hardended usercopy crap gets involved.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2020-03-06 16:58 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-13 21:45 [PATCH v3 0/4] Implement FUTEX_WAIT_MULTIPLE operation André Almeida
2020-02-13 21:45 ` [PATCH v3 1/4] futex: Implement mechanism to wait on any of several futexes André Almeida
2020-02-28 19:07 ` Peter Zijlstra
2020-02-28 19:49 ` Peter Zijlstra
2020-02-28 21:25 ` Thomas Gleixner
2020-02-29 0:29 ` Pierre-Loup A. Griffais
2020-02-29 10:27 ` Thomas Gleixner
2020-03-03 2:47 ` Pierre-Loup A. Griffais
2020-03-03 12:00 ` 'simple' futex interface [Was: [PATCH v3 1/4] futex: Implement mechanism to wait on any of several futexes] Peter Zijlstra
2020-03-03 13:00 ` Florian Weimer
2020-03-03 13:21 ` Peter Zijlstra
2020-03-03 13:47 ` Florian Weimer
2020-03-03 15:01 ` Peter Zijlstra
2020-03-05 16:14 ` André Almeida
2020-03-05 16:25 ` Florian Weimer
2020-03-05 18:51 ` Peter Zijlstra
2020-03-06 16:57 ` David Laight [this message]
2020-02-13 21:45 ` [PATCH v3 2/4] selftests: futex: Add FUTEX_WAIT_MULTIPLE timeout test André Almeida
2020-02-13 21:45 ` [PATCH v3 3/4] selftests: futex: Add FUTEX_WAIT_MULTIPLE wouldblock test André Almeida
2020-02-13 21:45 ` [PATCH v3 4/4] selftests: futex: Add FUTEX_WAIT_MULTIPLE wake up test André Almeida
2020-02-19 16:27 ` [PATCH v3 0/4] Implement FUTEX_WAIT_MULTIPLE operation shuah
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