From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "André Almeida" <andrealmeid@collabora.com>,
"Nicholas Piggin" <npiggin@gmail.com>,
acme@kernel.org, "Andrey Semashev" <andrey.semashev@gmail.com>,
corbet@lwn.net, "Davidlohr Bueso" <dave@stgolabs.net>,
"Darren Hart" <dvhart@infradead.org>,
fweimer@redhat.com, joel@joelfernandes.org, kernel@collabora.com,
krisman@collabora.com, libc-alpha@sourceware.org,
linux-api@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-kselftest@vger.kernel.org, malteskarupke@fastmail.fm,
"Ingo Molnar" <mingo@redhat.com>,
pgriffais@valvesoftware.com, "Peter Oskolkov" <posk@posk.io>,
"Steven Rostedt" <rostedt@goodmis.org>,
shuah@kernel.org, "Thomas Gleixner" <tglx@linutronix.de>,
z.figura12@gmail.com
Subject: Re: [PATCH v4 00/15] Add futex2 syscalls
Date: Tue, 8 Jun 2021 16:57:55 +0200 [thread overview]
Message-ID: <20210608145755.pwfhqrqdqft47nbw@linutronix.de> (raw)
In-Reply-To: <YL99cR0H+7xgU8L1@hirez.programming.kicks-ass.net>
On 2021-06-08 16:23:45 [+0200], Peter Zijlstra wrote:
> There's more futex users than glibc, and some of them are really hurting
> because of the NUMA issue. Oracle used to (I've no idea what they do or
> do not do these days) use sysvsem because the futex hash table was a
> massive bottleneck for them.
>
> And as Nick said, other vendors are having the same problems.
I just wanted to do a brief summary of last events. The implementation
tglx did with the cookie resulting in a quick lookup did not have any
downsides except that the user-API had to change glibc couldn't. So if
we are back to square one why not start with that.
> And if you don't extend the futex to store the nid you put the waiter in
> (see all the problems above) you will have to do wakeups on all nodes,
> which is both slower than it is today, and scales possibly even worse.
>
> The whole numa-aware qspinlock saga is in part because of futex.
sure.
> That said; if we're going to do the whole futex-vector thing, we really
> do need a new interface, because the futex multiplex monster is about to
> crumble (see the fun wrt timeouts for example).
This might have been a series of unfortunate events leading to this. The
sad part is that glibc has a comment that the kernel does not support
this and nobody bother to change it (until recently).
> And if we're going to do a new interface, we ought to make one that can
> solve all these problems. Now, ideally glibc will bring forth some
> opinions, but if they don't want to play, we'll go back to the good old
> days of non-standard locking libraries.. we're halfway there already due
> to glibc not wanting to break with POSIX were we know POSIX was just
> dead wrong broken.
>
> See: https://github.com/dvhart/librtpi
I'm aware of that, I hacked on it, too :) This was the unfortunate
result of a ~8y old bug which was not fixed instead and part of the code
was rewritten and a bit-spinlock was added in user-land. You may
remember the discussion regarding spins in userland…
That said, REQUEUE_PI is no longer used by glibc.
Sebastian
next prev parent reply other threads:[~2021-06-08 14:58 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-03 19:59 [PATCH v4 00/15] Add futex2 syscalls André Almeida
2021-06-03 19:59 ` [PATCH v4 01/15] futex2: Implement wait and wake functions André Almeida
2021-06-03 19:59 ` [PATCH v4 02/15] futex2: Add support for shared futexes André Almeida
2021-06-03 19:59 ` [PATCH v4 03/15] futex2: Implement vectorized wait André Almeida
2021-06-03 19:59 ` [PATCH v4 04/15] futex2: Implement requeue operation André Almeida
2021-06-03 19:59 ` [PATCH v4 05/15] futex2: Implement support for different futex sizes André Almeida
2021-06-04 0:23 ` kernel test robot
2021-06-06 19:12 ` Davidlohr Bueso
2021-06-06 23:01 ` Andrey Semashev
2021-06-03 19:59 ` [PATCH v4 06/15] futex2: Add compatibility entry point for x86_x32 ABI André Almeida
2021-06-03 19:59 ` [PATCH v4 07/15] docs: locking: futex2: Add documentation André Almeida
2021-06-06 19:23 ` Davidlohr Bueso
2021-06-03 19:59 ` [PATCH v4 08/15] selftests: futex2: Add wake/wait test André Almeida
2021-06-03 19:59 ` [PATCH v4 09/15] selftests: futex2: Add timeout test André Almeida
2021-06-03 19:59 ` [PATCH v4 10/15] selftests: futex2: Add wouldblock test André Almeida
2021-06-03 19:59 ` [PATCH v4 11/15] selftests: futex2: Add waitv test André Almeida
2021-06-03 19:59 ` [PATCH v4 12/15] selftests: futex2: Add requeue test André Almeida
2021-06-03 19:59 ` [PATCH v4 13/15] selftests: futex2: Add futex sizes test André Almeida
2021-06-03 19:59 ` [PATCH v4 14/15] perf bench: Add futex2 benchmark tests André Almeida
2021-06-03 19:59 ` [PATCH v4 15/15] kernel: Enable waitpid() for futex2 André Almeida
2021-06-04 4:51 ` [PATCH v4 00/15] Add futex2 syscalls Zebediah Figura
2021-06-04 17:04 ` André Almeida
2021-06-04 11:36 ` Nicholas Piggin
2021-06-04 20:01 ` André Almeida
2021-06-05 1:09 ` Nicholas Piggin
2021-06-05 8:56 ` Andrey Semashev
2021-06-06 11:57 ` Nicholas Piggin
2021-06-06 13:15 ` Andrey Semashev
2021-06-08 1:25 ` Nicholas Piggin
2021-06-08 11:03 ` Andrey Semashev
2021-06-08 11:13 ` Greg KH
2021-06-08 11:44 ` Peter Zijlstra
2021-06-08 14:31 ` Davidlohr Bueso
2021-06-08 12:06 ` Andrey Semashev
2021-06-08 12:33 ` Greg KH
2021-06-08 12:35 ` Greg KH
2021-06-08 13:18 ` Andrey Semashev
2021-06-08 13:27 ` Greg KH
2021-06-08 13:41 ` Andrey Semashev
2021-06-08 17:06 ` Zebediah Figura
2021-06-08 14:14 ` André Almeida
2021-06-07 15:40 ` André Almeida
2021-06-08 1:31 ` Nicholas Piggin
2021-06-08 2:33 ` Davidlohr Bueso
2021-06-08 4:45 ` Nicholas Piggin
2021-06-08 12:26 ` Sebastian Andrzej Siewior
2021-06-08 14:23 ` Peter Zijlstra
2021-06-08 14:57 ` Sebastian Andrzej Siewior [this message]
2021-06-08 15:04 ` André Almeida
2021-06-08 18:08 ` Adhemerval Zanella
2021-06-08 18:19 ` Florian Weimer
2021-06-08 18:22 ` Adhemerval Zanella
2021-06-09 16:26 ` David Laight
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