linux-kernel - Re: [PATCH] cciss: Optimize scan

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Message-ID: <5539232F.4050404@kernel.dk>
Date:	Thu, 23 Apr 2015 10:51:59 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	Davidlohr Bueso <dave@...olabs.net>
CC:	Mike Miller <mike.miller@...com>, Don Brace <don.brace@...s.com>,
	iss_storagedev@...com, storagedev@...s.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cciss: Optimize scan_thread

On 04/22/2015 12:43 PM, Davidlohr Bueso wrote:
> Two rather small optimizations found while going through driver
> code:
>
> 1) Use the cheaper alternative to set_current_state() as we are
> sure the task will block right afterward.
>
> 2) Checks for list_empty without the scan_mutex. The list_empty
> function is very much designed to work without locks, obviously
> as long as the head (scan_q) is reliable. In this case if another
> thread is doing add_to_scan_list(), we still buckle in the outer
> loop, so it will be caught upon the next iteration -- and if
> kthread_should_stop() hits, it does not matter _anyway_ as we'd
> still need to abort the function regardless of the status of
> the scan_q.

Not that it's wrong, but this is mostly some unneeded optimizations. 
It's not like this is in a hot path.

-- 
Jens Axboe

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