linux-kernel - Re: [PATCH v2 1/4] blk-mq: use percpu csd to remote complete instead of per-rq csd

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Date:   Wed, 5 Jul 2023 23:01:02 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     chengming.zhou@...ux.dev
Cc:     axboe@...nel.dk, hch@....de, tj@...nel.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        Chengming Zhou <zhouchengming@...edance.com>
Subject: Re: [PATCH v2 1/4] blk-mq: use percpu csd to remote complete instead
 of per-rq csd

On Thu, Jun 29, 2023 at 07:03:56PM +0800, chengming.zhou@...ux.dev wrote:
> From: Chengming Zhou <zhouchengming@...edance.com>
> 
> If request need to be completed remotely, we insert it into percpu llist,
> and smp_call_function_single_async() if llist is empty previously.
> 
> We don't need to use per-rq csd, percpu csd is enough. And the size of
> struct request is decreased by 24 bytes.
> 
> This way is cleaner, and looks correct, given block softirq is guaranteed to be
> scheduled to consume the list if one new request is added to this percpu list,
> either smp_call_function_single_async() returns -EBUSY or 0.
> 
> Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
> ---
> v2:
>  - Change to use call_single_data_t, which avoid to use 2 cache lines
>    for 1 csd, as suggested by Ming Lei.
>  - Improve the commit log, the explanation is copied from Ming Lei.

Reviewed-by: Ming Lei <ming.lei@...hat.com>

Thanks,
Ming