Re: [PATCH 5/7] blk-mq: initialize request on allocation

[Ming Lei]

On Thu, Apr 17, 2014 at 10:57 PM, Christoph Hellwig <hch@xxxxxx> wrote:
> On Thu, Apr 17, 2014 at 10:54:23PM +0800, Ming Lei wrote:
>> On Mon, Apr 14, 2014 at 4:30 PM, Christoph Hellwig <hch@xxxxxx> wrote:
>> > If we want to share tag and request allocation between queues we cannot
>> > initialize the request at init/free time, but need to initialize it
>> > at allocation time as it might get used for different queues over its
>> > lifetime.
>>
>> Could you explain the use pattern? Looks you mean there are
>> still users of the tag/req even after it is freed, that looks a bit
>> weird since the tag/req can still be reallocated in another path
>> after it is freed.
>
> No difference in use pattern.  But blk_rq_init initializes the rq->q field,
> and a request might get reused for a different queue.

If so, it may be better to only initialize the rq->q in allocation
because Jens said 'It's done that way because of presumed cache
hotness on completion'.


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