From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from dggsgout12.his.huawei.com (dggsgout12.his.huawei.com [45.249.212.56]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1FE6F171E6E; Fri, 22 Nov 2024 08:16:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.56 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732263378; cv=none; b=cNRY9vz0fZfh9rOFWIRHGGLIhBhZb0oVc5zEpCB3FdrKjGv3isdFt1OQED1QtEbMZNDmnrWpqZzrdGirj/FbEPUSymU3D429Qg6IX/vvDAnRqBAnyJNC3F4DG8GYT+DV03dBJFmmE1M6iY4oWgMUtPq/GW+ZG86dsTNNr4xSpMA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732263378; c=relaxed/simple; bh=B/umVHltx40EK9tLtMFoyBigt7N5JcyxpAQHcxVBg2Y=; h=Subject:To:Cc:References:From:Message-ID:Date:MIME-Version: In-Reply-To:Content-Type; b=KcNeJbxvZsHzfEsPEVUtJsDQuz/r0f1hMi9gVhT5NQgVdmZG8HBs26fpLAMfxCgPUYo4fhdkSilyGCp4jcqZDzCtaqT5V16YQxczGstRZudvpSmP1+h6rAp6Vb8y7XyNHbP4bltB8Q6gjS+Msz4411sjH6KlqjP6Z+3TXbvEJ74= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=huaweicloud.com; spf=pass smtp.mailfrom=huaweicloud.com; arc=none smtp.client-ip=45.249.212.56 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=huaweicloud.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huaweicloud.com Received: from mail.maildlp.com (unknown [172.19.93.142]) by dggsgout12.his.huawei.com (SkyGuard) with ESMTP id 4Xvnwl2Q3sz4f3jYB; Fri, 22 Nov 2024 16:15:51 +0800 (CST) Received: from mail02.huawei.com (unknown [10.116.40.128]) by mail.maildlp.com (Postfix) with ESMTP id E05841A07B6; Fri, 22 Nov 2024 16:16:09 +0800 (CST) Received: from [10.174.176.73] (unknown [10.174.176.73]) by APP4 (Coremail) with SMTP id gCh0CgB3U4fIPUBnhmj+CQ--.60080S3; Fri, 22 Nov 2024 16:16:09 +0800 (CST) Subject: Re: [PATCH] block: iocost: ensure hweight_inuse is at least 1 To: Kunhai Dai , tj@kernel.org, josef@toxicpanda.com, axboe@kernel.dk Cc: cgroups@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, "yukuai (C)" References: <20241122072609.29429-1-daikunhai@didiglobal.com> From: Yu Kuai Message-ID: <29ebfb70-87de-dd75-5ff2-0ca49ec35cf1@huaweicloud.com> Date: Fri, 22 Nov 2024 16:16:07 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: <20241122072609.29429-1-daikunhai@didiglobal.com> Content-Type: text/plain; charset=gbk; format=flowed Content-Transfer-Encoding: 8bit X-CM-TRANSID:gCh0CgB3U4fIPUBnhmj+CQ--.60080S3 X-Coremail-Antispam: 1UD129KBjvJXoW7Cry3WFWxAw15Zw1kWFykZrb_yoW8Wr4kpr y5W3WYyry7GF4I93WrKw1jkw15Zws3WF4Iqrnav3y3Cr4xJ3sIkr4xJr4DGa4rXrs3Xr4I qr17tFy8G3y3Cr7anT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUvjb4IE77IF4wAFF20E14v26r4j6ryUM7CY07I20VC2zVCF04k2 6cxKx2IYs7xG6rWj6s0DM7CIcVAFz4kK6r1j6r18M28lY4IEw2IIxxk0rwA2F7IY1VAKz4 vEj48ve4kI8wA2z4x0Y4vE2Ix0cI8IcVAFwI0_Ar0_tr1l84ACjcxK6xIIjxv20xvEc7Cj xVAFwI0_Gr1j6F4UJwA2z4x0Y4vEx4A2jsIE14v26rxl6s0DM28EF7xvwVC2z280aVCY1x 0267AKxVW0oVCq3wAS0I0E0xvYzxvE52x082IY62kv0487Mc02F40EFcxC0VAKzVAqx4xG 6I80ewAv7VC0I7IYx2IY67AKxVWUGVWUXwAv7VC2z280aVAFwI0_Jr0_Gr1lOx8S6xCaFV Cjc4AY6r1j6r4UM4x0Y48IcVAKI48JMxk0xIA0c2IEe2xFo4CEbIxvr21lc7CjxVAaw2AF wI0_JF0_Jw1l42xK82IYc2Ij64vIr41l4I8I3I0E4IkC6x0Yz7v_Jr0_Gr1lx2IqxVAqx4 xG67AKxVWUJVWUGwC20s026x8GjcxK67AKxVWUGVWUWwC2zVAF1VAY17CE14v26r1q6r43 MIIYrxkI7VAKI48JMIIF0xvE2Ix0cI8IcVAFwI0_Jr0_JF4lIxAIcVC0I7IYx2IY6xkF7I 0E14v26r4j6F4UMIIF0xvE42xK8VAvwI8IcIk0rVWUJVWUCwCI42IY6I8E87Iv67AKxVWU JVW8JwCI42IY6I8E87Iv6xkF7I0E14v26r4j6r4UJbIYCTnIWIevJa73UjIFyTuYvjxUot CzDUUUU X-CM-SenderInfo: 51xn3trlr6x35dzhxuhorxvhhfrp/ Hi, ÔÚ 2024/11/22 15:26, Kunhai Dai дµÀ: > The hweight_inuse calculation in transfer_surpluses() could potentially > result in a value of 0, which would lead to division by zero errors in > subsequent calculations that use this value as a divisor. > > Signed-off-by: Kunhai Dai > --- > block/blk-iocost.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/block/blk-iocost.c b/block/blk-iocost.c > index 384aa15e8260..65cdb55d30cc 100644 > --- a/block/blk-iocost.c > +++ b/block/blk-iocost.c > @@ -1999,9 +1999,10 @@ static void transfer_surpluses(struct list_head *surpluses, struct ioc_now *now) > parent = iocg->ancestors[iocg->level - 1]; > > /* b' = gamma * b_f + b_t' */ > - iocg->hweight_inuse = DIV64_U64_ROUND_UP( > - (u64)gamma * (iocg->hweight_active - iocg->hweight_donating), > - WEIGHT_ONE) + iocg->hweight_after_donation; > + iocg->hweight_inuse = max_t(u64, 1, > + DIV64_U64_ROUND_UP( > + (u64)gamma * (iocg->hweight_active - iocg->hweight_donating), > + WEIGHT_ONE) + iocg->hweight_after_donation); I'm confused, how could DIV64_U64_Round_UP() end up less than 1? #define DIV64_U64_ROUND_UP(ll, d) \ ({ u64 _tmp = (d); div64_u64((ll) + _tmp - 1, _tmp); }) AFAIK, the only case that could happen is that iocg->hweight_active - iocg->hweight_donating is 0, then I don't get it now how cound active iocg donate all the hweight, if this really happend perhaps the better solution is to avoid such case. Thanks, Kuai > > /* w' = s' * b' / b'_p */ > inuse = DIV64_U64_ROUND_UP( >