From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 E58372F3B for ; Fri, 21 Feb 2025 02:55:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740106543; cv=none; b=U9cXaJ/KXXvO+1/LRfZrjeK+vjsLpxLH4GU4+NZmBknBrazgoLcCarYI9rHJaWOJnWXotkEK/no6yRUr6RlFQw6tg/oSYTz7NvOxT33C/QnO/Yavob846T/Mcfkgtgdkzygdj8x4g21Yhqvi0DdRv9CK5ID4irj1iRYxlA5bX2s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740106543; c=relaxed/simple; bh=yA9yb+v/RyQTqipBCXHv1BDNck+KMt9TAtL4IzWZgJY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=I7UA3+eTXRqhqmGISt+tmdl7N/+4St+9CviPAc20wMg8MqADG6SeumvnH4N4CwAdMNxPhGtL/+x1Gmc22Bbj3vTbbODj/p8lsuwU/cwE3nEWrnS1T9/EGywxiJwXcB2MTsxjXSyThIdS3G82uyQBbw6/f8XTVI2Qxq1KsMfqzW4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=YtgTFrWI; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="YtgTFrWI" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1740106540; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=1mVTzm9GkpidsK39/v1CuCMhdkhioOej4w+t01AWWV8=; b=YtgTFrWI7PWkJGwujhh9bwa4zxPum+nbWxf+e5E4L9SFD8enfcolsm6ObJS6l21fu1Ga4O Z50rhgXVr0HcrxEZ+11F5NXiQecTnx5kSQhWQaiyM4eaDh165u9sWKb6uSIiMb/52Nnerq xRWisXRySnBBrITwrbuRYQgqjnqT0bo= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-37-sXRCsVUxOYWV5ca3R50Rvw-1; Thu, 20 Feb 2025 21:55:37 -0500 X-MC-Unique: sXRCsVUxOYWV5ca3R50Rvw-1 X-Mimecast-MFC-AGG-ID: sXRCsVUxOYWV5ca3R50Rvw_1740106534 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id B228D1800873; Fri, 21 Feb 2025 02:55:33 +0000 (UTC) Received: from fedora (unknown [10.72.120.9]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 3476C1955BCB; Fri, 21 Feb 2025 02:55:28 +0000 (UTC) Date: Fri, 21 Feb 2025 10:55:23 +0800 From: Ming Lei To: Yu Kuai Cc: Jens Axboe , linux-block@vger.kernel.org, Tejun Heo , "yukuai (C)" Subject: Re: [PATCH] block: throttle: don't add one extra jiffy mistakenly for bps limit Message-ID: References: <20250220111735.1187999-1-ming.lei@redhat.com> Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 Hi Yukuai, On Thu, Feb 20, 2025 at 09:38:12PM +0800, Yu Kuai wrote: > Hi, > > 在 2025/02/20 19:17, Ming Lei 写道: > > When the current bio needs to be throttled because of bps limit, the wait > > time for the extra bytes may be less than 1 jiffy, tg_within_bps_limit() > > adds one extra 1 jiffy. > > > > However, when taking roundup time into account, the extra 1 jiffy > > may become not necessary, then bps limit becomes not accurate. This way > > causes blktests throtl/001 failure in case of CONFIG_HZ_100=y. > > > > Fix it by not adding the 1 jiffy in case that the roundup time can > > cover it. > > > > Cc: Tejun Heo > > Cc: Yu Kuai > > Signed-off-by: Ming Lei > > --- > > block/blk-throttle.c | 6 +++--- > > 1 file changed, 3 insertions(+), 3 deletions(-) > > > > diff --git a/block/blk-throttle.c b/block/blk-throttle.c > > index 8d149aff9fd0..8348972c517b 100644 > > --- a/block/blk-throttle.c > > +++ b/block/blk-throttle.c > > @@ -729,14 +729,14 @@ static unsigned long tg_within_bps_limit(struct throtl_grp *tg, struct bio *bio, > > extra_bytes = tg->bytes_disp[rw] + bio_size - bytes_allowed; > > jiffy_wait = div64_u64(extra_bytes * HZ, bps_limit); > > - if (!jiffy_wait) > > - jiffy_wait = 1; > > - > > /* > > * This wait time is without taking into consideration the rounding > > * up we did. Add that time also. > > */ > > jiffy_wait = jiffy_wait + (jiffy_elapsed_rnd - jiffy_elapsed); > > + if (!jiffy_wait) > > + jiffy_wait = 1; > > Just wonder, will wait (0, 1) less jiffies is better than wait (0, 1) > more jiffies. > > How about following changes? > > Thanks, > Kuai > > diff --git a/block/blk-throttle.c b/block/blk-throttle.c > index 8d149aff9fd0..f8430baf3544 100644 > --- a/block/blk-throttle.c > +++ b/block/blk-throttle.c > @@ -703,6 +703,7 @@ static unsigned long tg_within_bps_limit(struct > throtl_grp *tg, struct bio *bio, > u64 bps_limit) > { > bool rw = bio_data_dir(bio); > + long long carryover_bytes; > long long bytes_allowed; > u64 extra_bytes; > unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd; > @@ -727,10 +728,11 @@ static unsigned long tg_within_bps_limit(struct > throtl_grp *tg, struct bio *bio, > > /* Calc approx time to dispatch */ > extra_bytes = tg->bytes_disp[rw] + bio_size - bytes_allowed; > - jiffy_wait = div64_u64(extra_bytes * HZ, bps_limit); > + jiffy_wait = div64_u64_rem(extra_bytes * HZ, bps_limit, > carryover_bytes); > &carryover_bytes > + /* carryover_bytes is dispatched without waiting */ > if (!jiffy_wait) > - jiffy_wait = 1; > + tg->carryover_bytes[rw] -= carryover_bytes; > > /* > * This wait time is without taking into consideration the rounding > > > + > > return jiffy_wait; Looks result is worse with your patch: throtl/001 (basic functionality) [failed] runtime 6.488s ... 28.862s --- tests/throtl/001.out 2024-11-21 09:20:47.514353642 +0000 +++ /root/git/blktests/results/nodev/throtl/001.out.bad 2025-02-21 02:51:36.723754146 +0000 @@ -1,6 +1,6 @@ Running throtl/001 +13 1 -1 -1 +13 1 ... (Run 'diff -u tests/throtl/001.out /root/git/blktests/results/nodev/throtl/001.out.bad' to see the entire diff) thanks, Ming