![]() selftests/futex/functional/Makefile | 3 +. selftests/futex/functional/.gitignore | 1 + Selftests: futex2: Test futex_waitv timeoutĪrch/x86/entry/syscalls/syscall_32.tbl | 1 +Īrch/x86/entry/syscalls/syscall_64.tbl | 1 + Compat and non-compat entry point now uses the same code and same Splitted syscall table changes from the implementation Changed the struct to have explicit padding (thanks Arnd!) V1: Tons of code and comment improvements and fixes (thanks Thomas!) V2: Last version, I made compat and non-compat use the same code, butįailed to remove the compat entry point. The selftest, but I'm not sure if this the best from v2: In the past I implemented a gettime64() by myself as part of Platforms giving that glibc doesn't expose a way to have a 64-bit timespec However, those selftests aren't really reliable in 32-bit Through Proton, I've tested futex_waitv() with modern games that issue Support, the better the implementation can be in the standard library." Supports this for atomic variables of any size. ![]() Library" and "The C++ standard added futexes to the standard library inĬ++20 under the name atomic_wait and atomic_notify. The first reason WebKit mentioned for re-implementing futexes in a Use cases as well: "Having mutexes that are only one byte in size was The original proposal to support 8-bit and 16-bit futexes had some Makes it so that only one shared memory location needs to be accessed Producer/consumer scenario, with the producer updating some shared Useful to do atomic operations in pointer values: "imagine a simple Peter Oskolkov pointed out that for 64-bit platforms it would be Part of an atomically updated 64-bit word". ![]() glibc’s rwlock implementation "uses a torn 32-bit futex read which is Inter-process atomics, this means that waiting must be done using a spin It works fine for 32-bit futexes, butįor other sizes it "must use an internal lock pool to implement waitingĪnd notifying operations, which increases thread contention. At Boost Libraries, futex is used as back end to implement atomic uintptr_t does the tricky and it works forĪlthough futex() supports only 32-bit long integers, while researchingĪbout feedback around a new futex interface, developers made some points Userspace has 32-bit pointers, it should do a explicit cast to make sure The _reserved is used for the padding and should alwaysīe 0, but it may be repurposed in the future for some extension. Struct futex_waitv uses explicit padding, so we can use it in allĪrchitectures. Unsigned int flags, struct timespec *timo) Native game engines will benefit of this as well, given thatįutex_waitv(struct futex_waitv *waiters, unsigned int nr_futexes, Scale very well for a huge number of read, write and poll calls compared Compared to a solution that uses eventfd(),įutex was able to reduce CPU utilization for games, and even increaseįrames per second for some games. Has been used for some time at Proton's Wine (a compatibility layer to This is specially useful forĮmulating Windows' WaitForMultipleObjects. Wait for multiple locks at the same time. The use case of this syscall is to allow low level locking libraries to Possible of original futex code for the new operation, so the firstĬommit move some stuff to futex header to make accessible for futex2. This patchset introduce the futex_waitv syscall. Reply-To: =?utf-8?q?Andr=C3=A9_Almeida?= Ĭc: Davidlohr Bueso, =?utf-8?q?Andr=C3=A9_Alm?=įutex2: Add wait on multiple futexes syscallĪndré Almeida Sept. X-Spam-Checker-Version: SpamAssassin 3.4.4 () onįrom: =?utf-8?q?Andr=C3=A9_Almeida_via_Libc-alpha?= UNPARSEABLE_RELAY autolearn=no autolearn_force=no version=3.4.4 KAM_MANYTO, SPF_HELO_PASS, SPF_PASS, TXREP, X-Spam-Status: No, score=-6.1 required=5.0 tests=BAYES_00, KAM_DMARC_STATUS, Subject: futex2: Add wait on multiple futexes syscall Peter Zijlstra, Darren Hart Steven Rostedt , (Authenticated sender: tonyk) with ESMTPSA id 74EAD1F42CE5 SSiOD/1SFQ7txVdVCnXdTl6/QONmp/WTgXgJxuhw= JmHWV3DeIO/tX+l6FwPtnycvVWWpPDv7j8Iq7hOZn9mYwSFKK2GUJ9B4pzmeMT3VyX List-Help:List-Subscribe:From:Reply-To:Cc:From ī=PYbvEa+Z/jYWZI8ax4rvIulrdceJiO2Sl6jyREcQfJibMo7yhe7qksfVXTrdMnRCi H=To:Subject:Date:List-Id:List-Unsubscribe:List-Archive:List-Post: X-Original-To: from (localhost )īy (Postfix) with ESMTP id 65B613858031ĭKIM-Filter: OpenDKIM Filter v2.11.0 65B613858031ĭKIM-Signature: v=1 a=rsa-sha256 c=relaxed/relaxed d= īh=4qRU6wTzJgDe6RLQcYF7nuC5uOo6tuPwuqabaeyYeMI=
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