Message-ID: <5539232F.4050404@kernel.dk>
Date: Thu, 23 Apr 2015 10:51:59 -0600
From: Jens Axboe <axboe@kernel.dk>
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0
MIME-Version: 1.0
To: Davidlohr Bueso <dave@stgolabs.net>
CC: Mike Miller <mike.miller@hp.com>, Don Brace <don.brace@pmcs.com>,
        iss_storagedev@hp.com, storagedev@pmcs.com,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] cciss: Optimize scan_thread
References: <1429728220.10273.26.camel@stgolabs.net>
In-Reply-To: <1429728220.10273.26.camel@stgolabs.net>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1078
Lines: 27

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

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/