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 3FE0CC28D13 for ; Thu, 25 Aug 2022 11:55:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232349AbiHYLzN (ORCPT ); Thu, 25 Aug 2022 07:55:13 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59174 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238711AbiHYLzM (ORCPT ); Thu, 25 Aug 2022 07:55:12 -0400 Received: from mail-lf1-x12e.google.com (mail-lf1-x12e.google.com [IPv6:2a00:1450:4864:20::12e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8D192A260F for ; Thu, 25 Aug 2022 04:55:10 -0700 (PDT) Received: by mail-lf1-x12e.google.com with SMTP id m3so22194194lfg.10 for ; Thu, 25 Aug 2022 04:55:10 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc; bh=FfcOGEitlO1+VQU3Fkt40mgpPYh0aS/XS4OzrarjZWY=; b=YP8BXqIDz4FHk5I/P6OFRmLfnmAxmjh2ANz/mu2x1jmfIMQTmLpPcYxpNjq01ttb+E p0z+bpOQDg0GBKssTxzJLqaK8oyIcnZEHUad9X2NE1jnECS88d2SfIbK8HHHDCq8bo27 7kOMwba1NR/pBl/1VFnEcj1oNeM3djw4aiOdDV/8xcj2h5YoxyjI0BcTNduzkrNBrCMx xkflIuU93XGansAaaJgBHh6qVGGXJgkVowx3SB4/QbFqxt6ZKBh2gmpqqyXHY1PYaJ0O BDo1IhdCumtsP37ZO6h7vzmN+3FqhG3GHQEzOMgzN4O6NGE9enb5cWmhVoV2s7COJRYt p9Hw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc; bh=FfcOGEitlO1+VQU3Fkt40mgpPYh0aS/XS4OzrarjZWY=; b=zCu03kVFhZHS17W3RBiQAQe0VBHGHfn2NQh/1V3Va5FHRGmLCQtnV8aDPsL7SmGJ3N dxofBFknmyP6mrBi+pDJg4M0+fpUnjes1fWusAk+/+W2qaCfmzPkBkbppxb5DokuRrac KGCKDVp4qVAxj20bKXg37YHhaXN2b1Hd/wrLROGc64s1Q2QMMYlnb3pgF8l2IEp39EGO XkqgYe9OH56rZToxfT3PGbM7MblOOYC6XjDQJggzrclbMMEQCXmrwYITnzgQdxu2Lwsi 014ByGs1Do81mdm5Qy304OU4F4BlH1FI5YF8AyDoxKzykcdZ1Ubyx8WtkwkhYVGXigeZ kaOQ== X-Gm-Message-State: ACgBeo3N7MtHFaWqRXAsplfBYrQ0GoTwntaDgXz6jKvsD+eHHcxZTtaq xfl+u5k2Rj3S3BGlZh4FppQ= X-Google-Smtp-Source: AA6agR411kAkwEh29lG75CfMR95XCZoSa1SwdvQdBzbfRaR2acdWrqx3gpkMNciNmoF7qM1hHLfoVQ== X-Received: by 2002:a05:6512:3fa9:b0:492:d799:1038 with SMTP id x41-20020a0565123fa900b00492d7991038mr1066058lfa.574.1661428508894; Thu, 25 Aug 2022 04:55:08 -0700 (PDT) Received: from localhost (87-49-45-210-mobile.dk.customer.tdc.net. [87.49.45.210]) by smtp.gmail.com with ESMTPSA id o13-20020ac25b8d000000b0048af4dc964asm464973lfn.73.2022.08.25.04.55.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 25 Aug 2022 04:55:08 -0700 (PDT) Date: Thu, 25 Aug 2022 13:55:06 +0200 From: Pankaj Raghav To: Keith Busch Cc: axboe@kernel.dk, linux-block@vger.kernel.org, Keith Busch , Pankaj Raghav Subject: Re: [PATCHv2] sbitmap: fix batched wait_cnt accounting Message-ID: <20220825115506.nfwycdjkudwrob3q@quentin> References: <20220824201440.127782-1-kbusch@fb.com> <20220825114807.v5pjnkvtfttlsiv4@quentin> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220825114807.v5pjnkvtfttlsiv4@quentin> Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Thu, Aug 25, 2022 at 01:48:43PM +0200, Pankaj Raghav wrote: > On Wed, Aug 24, 2022 at 01:14:40PM -0700, Keith Busch wrote: > > > > -static bool __sbq_wake_up(struct sbitmap_queue *sbq) > > +static bool __sbq_wake_up(struct sbitmap_queue *sbq, int *nr) > > { > > struct sbq_wait_state *ws; > > - unsigned int wake_batch; > > - int wait_cnt; > > + int wake_batch, wait_cnt, sub, cur; > > > > ws = sbq_wake_ptr(sbq); > > if (!ws) > > return false; > > > > - wait_cnt = atomic_dec_return(&ws->wait_cnt); > > + wake_batch = READ_ONCE(sbq->wake_batch); > > + do { > > + cur = atomic_read(&ws->wait_cnt); > > I think the above statement is not needed if we use atomic_try_cmpxchg > as the old value is updated in that function itself. > https://docs.kernel.org/staging/index.html?highlight=atomic_try_cmpxchg#atomic-types I mean after moving the cur = atomic_read(..) above the do statement: wake_batch = READ_ONCE(sbq->wake_batch); cur = atomic_read(&ws->wait_cnt); do { sub = min3(wake_batch, *nr, cur); wait_cnt = cur - sub; } while (!atomic_try_cmpxchg(&ws->wait_cnt, &cur, wait_cnt)); -- Pankaj Raghav