linux-kernel - Re: [PATCH V3] blk-mq: count the hctx as active before allocate tag

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Message-ID: <3b980395-5030-34e0-7736-4a5227d8d860@kernel.dk>
Date:   Thu, 9 Aug 2018 08:35:25 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Jianchao Wang <jianchao.w.wang@...cle.com>
Cc:     tom.leiming@...il.com, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3] blk-mq: count the hctx as active before allocate tag

On 8/8/18 8:09 PM, Jianchao Wang wrote:
> Currently, we count the hctx as active after allocate driver tag
> successfully. If a previously inactive hctx try to get tag first
> time, it may fails and need to wait. However, due to the stale tag
> ->active_queues, the other shared-tags users are still able to
> occupy all driver tags while there is someone waiting for tag.
> Consequently, even if the previously inactive hctx is waked up, it
> still may not be able to get a tag and could be starved.
> 
> To fix it, we count the hctx as active before try to allocate driver
> tag, then when it is waiting the tag, the other shared-tag users
> will reserve budget for it.

Hand-applied for 4.19 (didn't apply directly).

-- 
Jens Axboe