From patchwork Thu Sep 8 15:12:00 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Uros Bizjak X-Patchwork-Id: 12970247 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 C02B2C54EE9 for ; Thu, 8 Sep 2022 15:12:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232866AbiIHPMM (ORCPT ); Thu, 8 Sep 2022 11:12:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48530 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232853AbiIHPMM (ORCPT ); Thu, 8 Sep 2022 11:12:12 -0400 Received: from mail-wr1-x430.google.com (mail-wr1-x430.google.com [IPv6:2a00:1450:4864:20::430]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 24210F3BC2; Thu, 8 Sep 2022 08:12:11 -0700 (PDT) Received: by mail-wr1-x430.google.com with SMTP id bz13so23209255wrb.2; Thu, 08 Sep 2022 08:12:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date; bh=Jp4krbitKaSk3RuEG4IHxarQ8BEhF9SZnO8KJfaZOzQ=; b=Tpk0PF1q6SYjUGrK3EigOTmQTwHqAb4d90j75ihUrn7+vgUOMF9frOB81lz7pFmYOG r+jFHHtndpaU+goPAGL25OEry8EejHkuck675GabFSu5pMIP0nS3xQvZdKF0eAZm5Z3P Wykiv7muRW5qszhWZfuoZo63RALITzi0v7tcJmezwhHUF4TqWjYC4kvnA1QtQXTLIr4m GCfzuIY2G8Y4chiyZ76kpHKUkWCrWuI8+b0JH88Fho+xeEdgCGKaClDYytyME88JvZzG uOQrnY3LxXThBSokwjVH8rSjmdahy0HoxdR14LBeGPGLYk/Jp9yAufJ3ce2xb3+O63v7 ZoOg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date; bh=Jp4krbitKaSk3RuEG4IHxarQ8BEhF9SZnO8KJfaZOzQ=; b=Htl803p4VWzd9vol7iEioUzE6XTG4lb5aJ9orU03Wf/vLH7YAuE37DYUmD/QgRGj3J WEdPjVySoHQkIv+EdaYS43je/tSBtQLyz4z3TXPagxDGXV4dGnnrf+pD4wwjW7vGorfQ o74XO2G+814W9sIxj/9bsV+pz07vyjyK+8XGPo0WfLpuHdcOsSdPOvSkXxQYtrjYBtVJ QATT6BloCUhIfbvR7ihfyVqkejWaVXb9sxrrftLVVzVq7V3AAkcgKIweD3SroWoHN3ZK HmSCmO+0yFms7pwReD2w0Swhe88OZ+KewnOVd8+92TfF2YB800Pmon8xkALUC6Siwbr5 XtpQ== X-Gm-Message-State: ACgBeo1Uq+AlqPA3Zw7SvGR6BQpAQHtDSFa+PEV9z2B2+yj4AxAoCwIv Crx1RQbJKyeD5yjwv4pcNYePAXwSCR9X6Q== X-Google-Smtp-Source: AA6agR6lXVUYvGPiufbzf6DzUFL4TM9V23eLsPTLwoHkX3OEB32hrswGY0TLrfGg2/7vkjTqckEvXA== X-Received: by 2002:a5d:650e:0:b0:228:b09e:de9a with SMTP id x14-20020a5d650e000000b00228b09ede9amr5724814wru.360.1662649929253; Thu, 08 Sep 2022 08:12:09 -0700 (PDT) Received: from localhost.localdomain ([46.248.82.114]) by smtp.gmail.com with ESMTPSA id v37-20020a05600c4da500b003b32b07f8f5sm2027460wmp.11.2022.09.08.08.12.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 08 Sep 2022 08:12:08 -0700 (PDT) From: Uros Bizjak To: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Uros Bizjak , Jens Axboe Subject: [PATCH RESEND v2] sbitmap: Use atomic_long_try_cmpxchg in __sbitmap_queue_get_batch Date: Thu, 8 Sep 2022 17:12:00 +0200 Message-Id: <20220908151200.9993-1-ubizjak@gmail.com> X-Mailer: git-send-email 2.37.2 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org Use atomic_long_try_cmpxchg instead of atomic_long_cmpxchg (*ptr, old, new) == old in __sbitmap_queue_get_batch. 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_long_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg fails, enabling further code simplifications, e.g. an extra memory read can be avoided in the loop. No functional change intended. Cc: Jens Axboe Signed-off-by: Uros Bizjak --- v2: Resend against linux-block for-6.1/block. --- lib/sbitmap.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/lib/sbitmap.c b/lib/sbitmap.c index a39b1a877366..299765a027bf 100644 --- a/lib/sbitmap.c +++ b/lib/sbitmap.c @@ -533,16 +533,16 @@ unsigned long __sbitmap_queue_get_batch(struct sbitmap_queue *sbq, int nr_tags, nr = find_first_zero_bit(&map->word, map_depth); if (nr + nr_tags <= map_depth) { atomic_long_t *ptr = (atomic_long_t *) &map->word; - unsigned long val, ret; + unsigned long val; get_mask = ((1UL << nr_tags) - 1) << nr; + val = READ_ONCE(map->word); do { - val = READ_ONCE(map->word); if ((val & ~get_mask) != val) goto next; - ret = atomic_long_cmpxchg(ptr, val, get_mask | val); - } while (ret != val); - get_mask = (get_mask & ~ret) >> nr; + } while (!atomic_long_try_cmpxchg(ptr, &val, + get_mask | val)); + get_mask = (get_mask & ~val) >> nr; if (get_mask) { *offset = nr + (index << sb->shift); update_alloc_hint_after_get(sb, depth, hint,