linux-kernel - Re: [PATCH] block: kyber: make kyber more friendly with merging

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Date:   Wed, 30 May 2018 16:36:32 +0800
From:   "jianchao.wang" <jianchao.w.wang@...cle.com>
To:     Ming Lei <tom.leiming@...il.com>
Cc:     Omar Sandoval <osandov@...ndov.com>, Jens Axboe <axboe@...nel.dk>,
        linux-block <linux-block@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] block: kyber: make kyber more friendly with merging

Hi ming

Thanks for your kindly response.

On 05/30/2018 04:22 PM, Ming Lei wrote:
>>> you could keep the software queues as-is but add our own version of
>>> flush_busy_ctxs() that only removes requests of the domain that we want.
>>> If one domain gets backed up, that might get messy with long iterations,
>>> though.
>> Yes, I also considered this approach :)
>> But the long iterations on every ctx->rq_list looks really inefficient.
> Right, this list can be quite long if dispatch token is used up.
> 
> You might try to introduce per-domain list into ctx directly, then 'none'
> may benefit from this change too since bio merge should be done
> on the per-domain list actually.

Yes, it maybe good for merging of 'none', because the rq_list is split into 3
lists, and not need to iterate the whole rq_list any more.
But what's about the dispatch when there is no io scheduler.
We will dispatch request from ctx one by one at the moment.
If we have per-domain list in ctx, we have to introduce some policies to determine
which domain to dispatch, and these policies should be in io scheduler actually.

Thanks
Jianchao