From nobody Wed Apr 8 04:31:29 2026 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 02785C32772 for ; Tue, 23 Aug 2022 17:27:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234804AbiHWR1d (ORCPT ); Tue, 23 Aug 2022 13:27:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58864 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236053AbiHWRZx (ORCPT ); Tue, 23 Aug 2022 13:25:53 -0400 Received: from mail-wr1-x42f.google.com (mail-wr1-x42f.google.com [IPv6:2a00:1450:4864:20::42f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2B7287D7B7; Tue, 23 Aug 2022 08:04:03 -0700 (PDT) Received: by mail-wr1-x42f.google.com with SMTP id r16so17346902wrm.6; Tue, 23 Aug 2022 08:04:03 -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; bh=UWD/zYOImijIaCRJjQ6Qdr+9a5CKuV8fnJ1O7aG/PXw=; b=dPG+yykmRC3fUMbUTYUtwPC8aaaIFXjBLd9EYlvJVTgwqkRac5HyYMpunGbqnj53tE 26KhntFBaodTiOj4py+G3Tz+h1kFdWKbYP5vEU9iRY6PX/2yNgdPLq+ftcHST8F2WxdQ fSezYvRysrN2CyOqUes7OC6qMr/fWJalQGpolw0S3rRWFdWu77Rh7uBu3KG0AAL0ntdd VK8jo5doaPdtQ6wOiY8/tQpT2H5JrDhbx0ztqGYb4VnKxAzeUT/pNWT9OBb+cx3nFuYV S9HiAr1OU4T4r1fRvyE7MXY4KgV7UMVe/kq5t6O8pdNiAn52Hc+g6SFDe/Ljm6yulib+ GwRw== 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; bh=UWD/zYOImijIaCRJjQ6Qdr+9a5CKuV8fnJ1O7aG/PXw=; b=Tcz7Q7Oggxq6KnvV6Ffzpb9HoIS8Q2gOwO/8LJ9uULCFte5sMWkB8A+eVj7wrRHEos iOZz3flL5ROwJDptp27jm3a/QSgYf+0me4yvC+fk/SxGG3g/I1cJ8quvobbGN2f8igoy 8ArYf+Oids0b7ti9muaMwfJ+L4DrnzwYRsSyP76JlKuVIhZgPkKpKnauP2MN0tMWhb4M u1IzdEzG+O8AfPNdAKk3UtHzdeBsIGfHh8iUyyYVKygDic0CC2K6aV/XNMrF8Y3cB3HF AnCRSjLZ8QpcW/HNQtPD6KeJyiyXOpwSz2NI448Abtay0U6zlqz5Vwyzv28KHWLm7BJN jHtg== X-Gm-Message-State: ACgBeo2EI0GIZm1oQTJTIpT7yO2UPujDYjdYBRfUbHM/pCqPE35CrXf9 LUjXyYWpVxobKHbYBg6hPNC5ridxsIEcyg== X-Google-Smtp-Source: AA6agR7/AJKDJ3fmGGjB2rFV9CtiSShlIbldfYUUc9bkFO95ho+PLDHlcvH1bMCehtEzHkEogVbHVg== X-Received: by 2002:a5d:5010:0:b0:225:611c:55fc with SMTP id e16-20020a5d5010000000b00225611c55fcmr4283164wrt.553.1661267041437; Tue, 23 Aug 2022 08:04:01 -0700 (PDT) Received: from localhost.localdomain ([46.248.82.114]) by smtp.gmail.com with ESMTPSA id bn26-20020a056000061a00b0021d7b41255esm14907690wrb.98.2022.08.23.08.04.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 23 Aug 2022 08:04:01 -0700 (PDT) From: Uros Bizjak To: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Uros Bizjak , Jens Axboe Subject: [PATCH] sbitmap: Use atomic_{,long}_try_cmpxchg in sbitmap.c Date: Tue, 23 Aug 2022 17:03:52 +0200 Message-Id: <20220823150352.3455-1-ubizjak@gmail.com> X-Mailer: git-send-email 2.37.1 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Use atomic_long_try_cmpxchg instead of atomic_long_cmpxchg (*ptr, old, new) =3D=3D old in __sbitmap_queue_get_batch and atomic_try_cmpxchg instead of atomic_cmpxchg (*ptr, old, new) =3D=3D old in __sbq_wake_up. 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. No functional change intended. Cc: Jens Axboe Signed-off-by: Uros Bizjak --- lib/sbitmap.c | 15 ++++++--------- 1 file changed, 6 insertions(+), 9 deletions(-) diff --git a/lib/sbitmap.c b/lib/sbitmap.c index 29eb0484215a..32392e65b98f 100644 --- a/lib/sbitmap.c +++ b/lib/sbitmap.c @@ -534,16 +534,16 @@ unsigned long __sbitmap_queue_get_batch(struct sbitma= p_queue *sbq, int nr_tags, if (nr + nr_tags <=3D map_depth) { atomic_long_t *ptr =3D (atomic_long_t *) &map->word; int map_tags =3D min_t(int, nr_tags, map_depth); - unsigned long val, ret; + unsigned long val; =20 get_mask =3D ((1UL << map_tags) - 1) << nr; + val =3D READ_ONCE(map->word); do { - val =3D READ_ONCE(map->word); if ((val & ~get_mask) !=3D val) goto next; - ret =3D atomic_long_cmpxchg(ptr, val, get_mask | val); - } while (ret !=3D val); - get_mask =3D (get_mask & ~ret) >> nr; + } while (!atomic_long_try_cmpxchg(ptr, &val, + get_mask | val)); + get_mask =3D (get_mask & ~val) >> nr; if (get_mask) { *offset =3D nr + (index << sb->shift); update_alloc_hint_after_get(sb, depth, hint, @@ -612,8 +612,6 @@ static bool __sbq_wake_up(struct sbitmap_queue *sbq) =20 wait_cnt =3D atomic_dec_return(&ws->wait_cnt); if (wait_cnt <=3D 0) { - int ret; - wake_batch =3D READ_ONCE(sbq->wake_batch); =20 /* @@ -628,8 +626,7 @@ static bool __sbq_wake_up(struct sbitmap_queue *sbq) * atomic_cmpxhcg() race should call this function again * to wakeup a new batch on a different 'ws'. */ - ret =3D atomic_cmpxchg(&ws->wait_cnt, wait_cnt, wake_batch); - if (ret =3D=3D wait_cnt) { + if (atomic_try_cmpxchg(&ws->wait_cnt, &wait_cnt, wake_batch)) { sbq_index_atomic_inc(&sbq->wake_index); wake_up_nr(&ws->wait, wake_batch); return false; --=20 2.37.1