linux-kernel - Re: [PATCH v5 1/3] block: Add support for reinsert a dispatched req

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Message-ID: <20130325123410.GG22327@kernel.dk>
Date:	Mon, 25 Mar 2013 06:34:10 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	Tanya Brokhman <tlinder@...eaurora.org>
Cc:	linux-mmc@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	Alex.Lemberg@...disk.com, open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 1/3] block: Add support for reinsert a dispatched req

On Mon, Mar 25 2013, Tanya Brokhman wrote:
> From: Tatyana Brokhman <tlinder@...eaurora.org>
> 
> Add support for reinserting a dispatched request back to the
> scheduler's internal data structures.
> This capability is used by the device driver when it chooses to
> interrupt the current request transmission and execute another (more
> urgent) pending request. For example: interrupting long write in order
> to handle pending read. The device driver re-inserts the
> remaining write request back to the scheduler, to be rescheduled
> for transmission later on.
> 
> Add API for verifying whether the current scheduler
> supports reinserting requests mechanism. If reinsert mechanism isn't
> supported by the scheduler, this code path will never be activated.

This is practically the exact same operation as a requeue. So why this
duplication? I also don't quite understand why an IO scheduler would
have to opt-in for this, seems like a pretty basic operation.

-- 
Jens Axboe

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