From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 9EA04145B1B for ; Wed, 15 May 2024 14:35:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1715783735; cv=none; b=oq3L+/VEsX4XWRaPkx0TiV+QgJtNhzSQJSGSc+GhDwbh7gZG3w7HPxoT364CdYLCsS1Gjx1aC3nsIcMWv8ZXVuHRZJ92NEZUBuuCt/8izeHNjP7gX1vhzEpCGvbqa/56KcaW4KOYevZBhAqazXCvZZtho9Xg9UuX8Xi5TBqkX7w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1715783735; c=relaxed/simple; bh=XrEHWXzHYH414DvlVESjOtx15TYA6noXORpfTNUMgRU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=cI5kPQDry9jasDTanKMDhMiutpjg9KEvOR3gxXoY44trCdPtzHGBndu4gqDS8DdZjGiKOA/k36KxWu1Qb6GP11guFwgUPNonVl+R1+CMQw58k/bh5rt9hjbw3/MisdEFJNUYgEW/Z+EzIn++vNZo8kDo6CF+HNffzR2W4sMtpOY= 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=gMa9qzSN; arc=none smtp.client-ip=170.10.133.124 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="gMa9qzSN" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1715783732; 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=Sc9fEb2mK7PfNta2o/2kA9lq5+CKKqFEWMN/clrZxT8=; b=gMa9qzSN9JgHLDoiJAPkm7Y0gcvUfxPye+lRniWKtjUwia44NYAHyx1PlQNoKpJqfsRIvw mHWKnrKzgUr1Fl4GGXavbY46q6gbDIoAaTeFT83ta8+GhKMoThWOrk8JRPLaZcn8NgNZ9J JuL+Ob6AkoKEy9zLi1+V356SbRRjuJU= Received: from mimecast-mx02.redhat.com (mx-ext.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-658-OvT26MQQMRis29XSB5ZWXA-1; Wed, 15 May 2024 10:35:21 -0400 X-MC-Unique: OvT26MQQMRis29XSB5ZWXA-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (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 mimecast-mx02.redhat.com (Postfix) with ESMTPS id 77A5D1C3F0EE; Wed, 15 May 2024 14:35:20 +0000 (UTC) Received: from [10.22.33.50] (unknown [10.22.33.50]) by smtp.corp.redhat.com (Postfix) with ESMTP id CD231200A08E; Wed, 15 May 2024 14:35:19 +0000 (UTC) Message-ID: <7ab67d43-84af-4328-8aca-9383afa2d6df@redhat.com> Date: Wed, 15 May 2024 10:35:19 -0400 Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] blk-cgroup: Properly propagate the iostat update up the hierarchy To: Jens Axboe , Tejun Heo , Josef Bacik Cc: cgroups@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Dan Schatzberg , Ming Lei References: <20240515143059.276677-1-longman@redhat.com> Content-Language: en-US From: Waiman Long In-Reply-To: <20240515143059.276677-1-longman@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.6 On 5/15/24 10:30, Waiman Long wrote: > During a cgroup_rstat_flush() call, the lowest level of nodes are flushed > first before their parents. Since commit 3b8cc6298724 ("blk-cgroup: > Optimize blkcg_rstat_flush()"), iostat propagation was still done to > the parent. Grandparent, however, may not get the iostat update if the > parent has no blkg_iostat_set queued in its lhead lockless list. > > Fix this iostat propagation problem by queuing the parent's global > blkg->iostat into one of its percpu lockless lists to make sure that > the delta will always be propagated up to the grandparent and so on > toward the root blkcg. > > Note that successive calls to __blkcg_rstat_flush() are serialized by > the cgroup_rstat_lock. So no special barrier is used in the reading > and writing of blkg->iostat.lqueued. > > Fixes: 3b8cc6298724 ("blk-cgroup: Optimize blkcg_rstat_flush()") > Reported-by: Dan Schatzberg > Closes: https://lore.kernel.org/lkml/ZkO6l%2FODzadSgdhC@dschatzberg-fedora-PF3DHTBV/ > Signed-off-by: Waiman Long > --- > block/blk-cgroup.c | 19 ++++++++++++++++++- > 1 file changed, 18 insertions(+), 1 deletion(-) > > diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c > index 059467086b13..2a7624c32a1a 100644 > --- a/block/blk-cgroup.c > +++ b/block/blk-cgroup.c > @@ -323,6 +323,7 @@ static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct gendisk *disk, > blkg->q = disk->queue; > INIT_LIST_HEAD(&blkg->q_node); > blkg->blkcg = blkcg; > + blkg->iostat.blkg = blkg; > #ifdef CONFIG_BLK_CGROUP_PUNT_BIO > spin_lock_init(&blkg->async_bio_lock); > bio_list_init(&blkg->async_bios); > @@ -1025,6 +1026,8 @@ static void __blkcg_rstat_flush(struct blkcg *blkcg, int cpu) > unsigned int seq; > > WRITE_ONCE(bisc->lqueued, false); > + if (bisc == &blkg->iostat) > + goto propagate_up; /* propagate up to parent only */ > > /* fetch the current per-cpu values */ > do { > @@ -1034,10 +1037,24 @@ static void __blkcg_rstat_flush(struct blkcg *blkcg, int cpu) > > blkcg_iostat_update(blkg, &cur, &bisc->last); > > +propagate_up: > /* propagate global delta to parent (unless that's root) */ > - if (parent && parent->parent) > + if (parent && parent->parent) { > blkcg_iostat_update(parent, &blkg->iostat.cur, > &blkg->iostat.last); > + /* > + * Queue parent->iostat to its blkcg's lockless > + * list to propagate up to the grandparent if the > + * iostat hasn't been queued yet. > + */ > + if (!parent->iostat.lqueued) { > + struct llist_head *plhead; > + > + plhead = per_cpu_ptr(parent->blkcg->lhead, cpu); > + llist_add(&parent->iostat.lnode, plhead); > + parent->iostat.lqueued = true; > + } > + } > } > raw_spin_unlock_irqrestore(&blkg_stat_lock, flags); > out: Note that this patch will conflict with Ming's patch (https://lore.kernel.org/linux-block/20240515013157.443672-3-ming.lei@redhat.com/). Will send out an updated version later on to synchronize with his patch. Cheers, Longman