From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id BCDD2C28D13 for ; Mon, 22 Aug 2022 20:47:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232096AbiHVUq7 (ORCPT ); Mon, 22 Aug 2022 16:46:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43350 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232069AbiHVUq6 (ORCPT ); Mon, 22 Aug 2022 16:46:58 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 40F0747B8B for ; Mon, 22 Aug 2022 13:46:57 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id CCFCB612E9 for ; Mon, 22 Aug 2022 20:46:56 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2BA67C433C1; Mon, 22 Aug 2022 20:46:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1661201216; bh=Ro7wXcYJeTRcIq8aJWywbsKARjKURsQYOzhHZUegv24=; h=Date:To:From:Subject:From; b=mBKVa8ntD9u69bR5vg2MZ+1IIQOg4b0qB7HqC3eeJNz0IZj36SN5eSNqcIPaaDKfq HCpQK6I9ngtjyNj9KjOd1JkauqJ6U/Y2uO93YuZvzNt1BdrHwc5L2C+oMlLqQKbnpd vuXhYxFBw1QaQOdkASY6w2zSfnDseASlfHmLF2Pg= Date: Mon, 22 Aug 2022 13:46:55 -0700 To: mm-commits@vger.kernel.org, ubizjak@gmail.com, akpm@linux-foundation.org From: Andrew Morton Subject: + bitops-use-try_cmpxchg-in-set_mask_bits-and-bit_clear_unless.patch added to mm-nonmm-unstable branch Message-Id: <20220822204656.2BA67C433C1@smtp.kernel.org> Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org The patch titled Subject: bitops: use try_cmpxchg in set_mask_bits and bit_clear_unless has been added to the -mm mm-nonmm-unstable branch. Its filename is bitops-use-try_cmpxchg-in-set_mask_bits-and-bit_clear_unless.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/bitops-use-try_cmpxchg-in-set_mask_bits-and-bit_clear_unless.patch This patch will later appear in the mm-nonmm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: Uros Bizjak Subject: bitops: use try_cmpxchg in set_mask_bits and bit_clear_unless Date: Mon, 22 Aug 2022 16:38:51 +0200 Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in set_mask_bits and bit_clear_unless. x86 CMPXCHG instruction returns success in ZF flag, so this change saves a compare after cmpxchg (and related move instruction in front of cmpxchg). Also, try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg fails, enabling further code simplifications. Link: https://lkml.kernel.org/r/20220822143851.3290-1-ubizjak@gmail.com Signed-off-by: Uros Bizjak Signed-off-by: Andrew Morton --- include/linux/bitops.h | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) --- a/include/linux/bitops.h~bitops-use-try_cmpxchg-in-set_mask_bits-and-bit_clear_unless +++ a/include/linux/bitops.h @@ -327,10 +327,10 @@ static __always_inline void __assign_bit const typeof(*(ptr)) mask__ = (mask), bits__ = (bits); \ typeof(*(ptr)) old__, new__; \ \ + old__ = READ_ONCE(*(ptr)); \ do { \ - old__ = READ_ONCE(*(ptr)); \ new__ = (old__ & ~mask__) | bits__; \ - } while (cmpxchg(ptr, old__, new__) != old__); \ + } while (!try_cmpxchg(ptr, &old__, new__)); \ \ old__; \ }) @@ -342,11 +342,12 @@ static __always_inline void __assign_bit const typeof(*(ptr)) clear__ = (clear), test__ = (test);\ typeof(*(ptr)) old__, new__; \ \ + old__ = READ_ONCE(*(ptr)); \ do { \ - old__ = READ_ONCE(*(ptr)); \ + if (old__ & test__) \ + break; \ new__ = old__ & ~clear__; \ - } while (!(old__ & test__) && \ - cmpxchg(ptr, old__, new__) != old__); \ + } while (!try_cmpxchg(ptr, &old__, new__)); \ \ !(old__ & test__); \ }) _ Patches currently in -mm which might be from ubizjak@gmail.com are llist-use-try_cmpxchg-in-llist_add_batch-and-llist_del_first.patch epoll-use-try_cmpxchg-in-list_add_tail_lockless.patch buffer-use-try_cmpxchg-in-discard_buffer.patch aio-use-atomic_try_cmpxchg-in-__get_reqs_available.patch iversion-use-atomic64_try_cmpxchg.patch bitops-use-try_cmpxchg-in-set_mask_bits-and-bit_clear_unless.patch