From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from dggsgout11.his.huawei.com (dggsgout11.his.huawei.com [45.249.212.51]) (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 2326A2135BC; Tue, 25 Feb 2025 03:12:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.51 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740453155; cv=none; b=j0dMcgLyGy1cIDV1MKqgnHuFTiF811pg50DjPf7DAWQRgXMaXdE43l76HX0Ra56HPnXFwwQztmW7aJwO8v/ssUvBEmzrqzyYqNxAMTd/3AhOmi6yLTk5L0cIHeywBHrojZnai0DmjKCvjHS0310zQyd44rH5aazA80+P54fJufA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740453155; c=relaxed/simple; bh=kjl+s6sWQ2AJgnYEcm8bFURklJKF/fJp4g1rYKQXWyM=; h=Subject:To:Cc:References:From:Message-ID:Date:MIME-Version: In-Reply-To:Content-Type; b=d4SSGtO727oXmgL6sOdPsf3QgDL5RgjnICGK/4NzDbKYYXZlhoOe+SXe2F39XU37zLa6qMis54WjoWF4SccPB68ffIJfHmgf8zizQcrhLurXtARbrScZz0mYP+EYadqBB7A1bMqRw4zE5qHmW6JYda7IMuptoiVwjEBvhkPOUmw= 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=45.249.212.51 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 dggsgout11.his.huawei.com (SkyGuard) with ESMTP id 4Z22hM5wt8z4f3kvf; Tue, 25 Feb 2025 11:12:03 +0800 (CST) Received: from mail02.huawei.com (unknown [10.116.40.128]) by mail.maildlp.com (Postfix) with ESMTP id 0FD1C1A0DCC; Tue, 25 Feb 2025 11:12:27 +0800 (CST) Received: from [10.174.179.143] (unknown [10.174.179.143]) by APP4 (Coremail) with SMTP id gCh0CgBHrGAZNb1nh_xKEw--.65158S3; Tue, 25 Feb 2025 11:12:26 +0800 (CST) Subject: Re: [PATCH 2/2] blk-throttle: fix off-by-one jiffies wait_time To: Ming Lei , Yu Kuai Cc: tj@kernel.org, josef@toxicpanda.com, axboe@kernel.dk, cgroups@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, yi.zhang@huawei.com, yangerkun@huawei.com, "yukuai (C)" References: <20250222092823.210318-1-yukuai1@huaweicloud.com> <20250222092823.210318-3-yukuai1@huaweicloud.com> <611f02a8-8430-16cf-46e5-e9417982b077@huaweicloud.com> <8473fca2-16ab-b2a6-ede7-d1449aa7d463@huaweicloud.com> From: Yu Kuai Message-ID: <084e25a1-5ed7-3097-5bae-b87addeaf01f@huaweicloud.com> Date: Tue, 25 Feb 2025 11:12:24 +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-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit X-CM-TRANSID:gCh0CgBHrGAZNb1nh_xKEw--.65158S3 X-Coremail-Antispam: 1UD129KBjvdXoW7Xr13Zw13Aw48uFWfCr4DJwb_yoWkXFX_uF 9xJwn3Cwn8CFn7uF4YkFy8K3y7Xr1Svry8C3yfGry7Z34IqFs7Z3WxGasa9ry2qa93X3Z0 vFn8AF1xGFn3WjkaLaAFLSUrUUUUjb8apTn2vfkv8UJUUUU8Yxn0WfASr-VFAUDa7-sFnT 9fnUUIcSsGvfJTRUUUbfAFF20E14v26r4j6ryUM7CY07I20VC2zVCF04k26cxKx2IYs7xG 6rWj6s0DM7CIcVAFz4kK6r1j6r18M28lY4IEw2IIxxk0rwA2F7IY1VAKz4vEj48ve4kI8w A2z4x0Y4vE2Ix0cI8IcVAFwI0_tr0E3s1l84ACjcxK6xIIjxv20xvEc7CjxVAFwI0_Gr1j 6F4UJwA2z4x0Y4vEx4A2jsIE14v26rxl6s0DM28EF7xvwVC2z280aVCY1x0267AKxVW0oV Cq3wAS0I0E0xvYzxvE52x082IY62kv0487Mc02F40EFcxC0VAKzVAqx4xG6I80ewAv7VC0 I7IYx2IY67AKxVWUJVWUGwAv7VC2z280aVAFwI0_Jr0_Gr1lOx8S6xCaFVCjc4AY6r1j6r 4UM4x0Y48IcVAKI48JM4x0x7Aq67IIx4CEVc8vx2IErcIFxwACI402YVCY1x02628vn2kI c2xKxwCYjI0SjxkI62AI1cAE67vIY487MxkF7I0En4kS14v26r1q6r43MxAIw28IcxkI7V AKI48JMxC20s026xCaFVCjc4AY6r1j6r4UMI8I3I0E5I8CrVAFwI0_Jr0_Jr4lx2IqxVCj r7xvwVAFwI0_JrI_JrWlx4CE17CEb7AF67AKxVWUtVW8ZwCIc40Y0x0EwIxGrwCI42IY6x IIjxv20xvE14v26r1j6r1xMIIF0xvE2Ix0cI8IcVCY1x0267AKxVW8JVWxJwCI42IY6xAI w20EY4v20xvaj40_Jr0_JF4lIxAIcVC2z280aVAFwI0_Jr0_Gr1lIxAIcVC2z280aVCY1x 0267AKxVW8JVW8JrUvcSsGvfC2KfnxnUUI43ZEXa7VUbGQ6JUUUUU== X-CM-SenderInfo: 51xn3trlr6x35dzhxuhorxvhhfrp/ Hi, Ming! 在 2025/02/25 10:28, Ming Lei 写道: > Can you explain in details why it signals that the rate is expected now? > > If rate isn't expected, it will cause trouble to trim, even just the > previous part. Ok, for example, assume bps_limit is 1000bytes, 1 jiffes is 10ms, and slice is 20ms(2 jiffies). expected rate is 1000 / 1000 * 20 = 20 bytes per slice. If user issue two 21 bytes IO, then wait time will be 30ms: bytes_allowed = 20, extra_bytes = 1; jiffy_wait = 1 + 2 = 3 jiffies and consider extra 1 jiffies by timer, throtl_trim_slice() will be called at: jiffies = 40ms slice_start = 0ms, slice_end= 40ms bytes_disp = 21 In this case, before the patch, real rate in the first two slice is is 10.5 bytes per slice, and slice will be updated: jiffies = 40ms slice_start = 40ms, slice_end = 60ms, bytes_disp = 0; Hence the second IO will have to wait another 30ms; With the patch, the real rate in the first slice is 20 bytes per slice, which is the same as expected, and slice will be updated: jiffies=40ms, slice_start = 20ms, slice_end = 60ms, bytes_disp = 1; And now, the second IO will only have to wait 10ms; Thanks, Kuai