From: Adhemerval Zanella via Libc-alpha <libc-alpha@sourceware.org>
To: Kurt Kanzenbach <kurt@linutronix.de>, libc-alpha@sourceware.org
Cc: Florian Weimer <fweimer@redhat.com>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
Joseph Myers <joseph@codesourcery.com>
Subject: Re: [PATCH v1 0/6] nptl: Introduce and use FUTEX_LOCK_PI2
Date: Fri, 9 Jul 2021 10:30:39 -0300 [thread overview]
Message-ID: <8b3c3bc1-1738-9b05-4557-776f31430cb5@linaro.org> (raw)
In-Reply-To: <20210625081104.1134598-1-kurt@linutronix.de>
On 25/06/2021 05:10, Kurt Kanzenbach wrote:
> Linux real time applications often make use of mutexes with priority inheritance
> enabled due to problems such as unbounded priority inversion. In addition, some
> applications make use of timeouts e.g., by utilizing pthread_mutex_clocklock().
>
> However, the combination of priority inheritance enabled mutexes with timeouts
> based on CLOCK_MONOTONIC doesn't work. That is because the underlying Linux
> kernel futex interface didn't support it, yet. Using CLOCK_REALTIME is possible,
> but it is subject to adjustments (NTP, PTP, ...). Therefore, Thomas proposed and
> introduced a new futex operation called FUTEX_LOCK_PI2 with support for
> selectable clocks [1].
>
> Here is a proof of concept patch set adding FUTEX_LOCK_PI2 in order to support
> pthread_mutex_clocklock(MONOTONIC)/PI. The idea is to use futex_lock_pi2() by
> default, and fallback to futex_lock_pi() in case the kernel is too old.
>
> There's also a bugreport for glibc with a test case:
>
> https://sourceware.org/bugzilla/show_bug.cgi?id=26801
>
> Changes since RFC:
>
> * FUTEX_LOCK_PI2 merged in upstream Linux kernel (Thomas Gleixner, Peter Zijlstra)
> * Make of __ASSUME_FUTEX_LOCK_PI2 in the implementation (Adhemerval Zanella)
> * Get rid of probing for FUTEX_LOCK_PI2 in timedlock (Adhemerval Zanella)
> * Adjust the test cases (Adhemerval Zanella)
> * Use correct Linux kernel version (Joseph Myers)
>
> Previous versions:
>
> * https://sourceware.org/pipermail/libc-alpha/2021-June/127798.html
>
> Thanks,
> Kurt
>
> [1] - https://lkml.kernel.org/lkml/20210422194417.866740847@linutronix.de/
Patch looks ok in general, I think I have only minor comments. I see that
FUTEX_LOCK_PI2 is already on Linus tree, should it should be safe to assume
it will on v5.14 (although is not yet released).
We are in the slush freeze for the 2.34 release, so you would like to check
with Carlos O'Donell if this set is suitable to inclusion. It does not
change any ABI, but I will need to some time to boot a kernel to actually
test it.
next prev parent reply other threads:[~2021-07-09 13:31 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-25 8:10 [PATCH v1 0/6] nptl: Introduce and use FUTEX_LOCK_PI2 Kurt Kanzenbach via Libc-alpha
2021-06-25 8:10 ` [PATCH v1 1/6] Linux: Add FUTEX_LOCK_PI2 Kurt Kanzenbach via Libc-alpha
2021-07-09 13:32 ` Adhemerval Zanella via Libc-alpha
2021-06-25 8:11 ` [PATCH v1 2/6] nptl: Introduce futex_lock_pi2() Kurt Kanzenbach via Libc-alpha
2021-07-09 14:13 ` Adhemerval Zanella via Libc-alpha
2021-06-25 8:11 ` [PATCH v1 3/6] nptl: Use futex_lock_pi2() Kurt Kanzenbach via Libc-alpha
2021-07-09 14:21 ` Adhemerval Zanella via Libc-alpha
2021-06-25 8:11 ` [PATCH v1 4/6] nptl: Remove mutex test 10 Kurt Kanzenbach via Libc-alpha
2021-07-09 14:23 ` Adhemerval Zanella via Libc-alpha
2021-06-25 8:11 ` [PATCH v1 5/6] nptl: mutex-test5: Include CLOCK_MONOTONIC for PI Kurt Kanzenbach via Libc-alpha
2021-06-25 8:11 ` [PATCH v1 6/6] nptl: mutex-test9: " Kurt Kanzenbach via Libc-alpha
2021-07-09 6:57 ` [PATCH v1 0/6] nptl: Introduce and use FUTEX_LOCK_PI2 Kurt Kanzenbach via Libc-alpha
2021-07-09 13:30 ` Adhemerval Zanella via Libc-alpha [this message]
2021-07-09 14:20 ` Kurt Kanzenbach via Libc-alpha
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