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 04D61ECAAA3 for ; Fri, 26 Aug 2022 01:54:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229990AbiHZByV (ORCPT ); Thu, 25 Aug 2022 21:54:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35114 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231532AbiHZByU (ORCPT ); Thu, 25 Aug 2022 21:54:20 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 28EC2C7F9B for ; Thu, 25 Aug 2022 18:54:16 -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 B097161DFD for ; Fri, 26 Aug 2022 01:54:15 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 146FDC433D6; Fri, 26 Aug 2022 01:54:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1661478855; bh=ACbaWK0JXC6Xb4Nm2fK2C1VzBO0x+laDSX83mD4v5P4=; h=Date:To:From:Subject:From; b=mzEkiugLoehbvKwlHl07g5+K3+zpvceBhP/x1m+71QWBqrWlXncTTOJnhUm0GEqY3 YRZAU0IhA8+EqKeks/sJzeOF8CPl8E8AsmFqS90RocPDWpkOGxAeP2tp1Hk5eAy/HM OMUQbCs7KRawp279CTeFtHmufPUN/fDV4z6u4ttQ= Date: Thu, 25 Aug 2022 18:54:14 -0700 To: mm-commits@vger.kernel.org, ubizjak@gmail.com, akpm@linux-foundation.org From: Andrew Morton Subject: + smpboot-use-atomic_try_cmpxchg-in-cpu_wait_death-and-cpu_report_death.patch added to mm-nonmm-unstable branch Message-Id: <20220826015415.146FDC433D6@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: smpboot: use atomic_try_cmpxchg in cpu_wait_death and cpu_report_death has been added to the -mm mm-nonmm-unstable branch. Its filename is smpboot-use-atomic_try_cmpxchg-in-cpu_wait_death-and-cpu_report_death.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/smpboot-use-atomic_try_cmpxchg-in-cpu_wait_death-and-cpu_report_death.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: smpboot: use atomic_try_cmpxchg in cpu_wait_death and cpu_report_death Date: Thu, 25 Aug 2022 16:56:03 +0200 Use atomic_try_cmpxchg instead of atomic_cmpxchg (*ptr, old, new) == old in cpu_wait_death and cpu_report_death. 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, atomic_try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg fails, enabling further code simplifications. No functional change intended. Link: https://lkml.kernel.org/r/20220825145603.5811-1-ubizjak@gmail.com Signed-off-by: Uros Bizjak Signed-off-by: Andrew Morton --- kernel/smpboot.c | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-) --- a/kernel/smpboot.c~smpboot-use-atomic_try_cmpxchg-in-cpu_wait_death-and-cpu_report_death +++ a/kernel/smpboot.c @@ -433,7 +433,7 @@ bool cpu_wait_death(unsigned int cpu, in /* The outgoing CPU will normally get done quite quickly. */ if (atomic_read(&per_cpu(cpu_hotplug_state, cpu)) == CPU_DEAD) - goto update_state; + goto update_state_early; udelay(5); /* But if the outgoing CPU dawdles, wait increasingly long times. */ @@ -444,16 +444,17 @@ bool cpu_wait_death(unsigned int cpu, in break; sleep_jf = DIV_ROUND_UP(sleep_jf * 11, 10); } -update_state: +update_state_early: oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu)); +update_state: if (oldstate == CPU_DEAD) { /* Outgoing CPU died normally, update state. */ smp_mb(); /* atomic_read() before update. */ atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_POST_DEAD); } else { /* Outgoing CPU still hasn't died, set state accordingly. */ - if (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu), - oldstate, CPU_BROKEN) != oldstate) + if (!atomic_try_cmpxchg(&per_cpu(cpu_hotplug_state, cpu), + &oldstate, CPU_BROKEN)) goto update_state; ret = false; } @@ -475,14 +476,14 @@ bool cpu_report_death(void) int newstate; int cpu = smp_processor_id(); + oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu)); do { - oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu)); if (oldstate != CPU_BROKEN) newstate = CPU_DEAD; else newstate = CPU_DEAD_FROZEN; - } while (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu), - oldstate, newstate) != oldstate); + } while (!atomic_try_cmpxchg(&per_cpu(cpu_hotplug_state, cpu), + &oldstate, newstate)); return newstate == CPU_DEAD; } _ 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 task_work-use-try_cmpxchg-in-task_work_add-task_work_cancel_match-and-task_work_run.patch smpboot-use-atomic_try_cmpxchg-in-cpu_wait_death-and-cpu_report_death.patch