2012/8/8 Jianpeng Ma <majianp...@gmail.com>:
> On 2012-08-08 11:06 Shaohua Li <s...@kernel.org> Wrote:
>>2012/8/8 Jianpeng Ma <majianp...@gmail.com>:
>>> I think there are three problems about handling plug in blk_queue_bio():
>>> 1:if request_count >= BLK_MAX_REQUEST_COUNT, avoid unnecessary
>>> plug->should_sort judge.
>>this makes sense, though not a big deal, nice to fix it.
> Thanks
>>
>>> 2:Only two device can trace plug.
>>I didn't get the point, can you have more details?
>
>>>if (plug) {
>>> /*
>>> * If this is the first request added after a plug, fire
>>> * of a plug trace. If others have been added before, check
>>> * if we have multiple devices in this plug. If so, make a
>>> * note to sort the list before dispatch.
>>> */
>>> if (list_empty(&plug->list))
>>> trace_block_plug(q);
>>> else {
>>> if (!plug->should_sort) {
>>> struct request *__rq;
>
>>> __rq = list_entry_rq(plug->list.prev);
>>> if (__rq->q != q)
>>> plug->should_sort = 1;
>>> }
>>> if (request_count >= BLK_MAX_REQUEST_COUNT) {
>>> blk_flush_plug_list(plug, false);
>>> trace_block_plug(q);
> The code only trace two point;
> A: list_empty(&plug->list)
> B: request_count >= BLK_MAX_REQUEST_COUNT). it's the same like A which
> plug->list is empty.
> Suppose:
> 1;reqA-deviceA firstly come, it will call trace_block_plug because the
> list_empty(plug->list) is true.
> 2:reqB-deviceB comed, attempt_plug_merge will failed because not
> deviceB-request-queue.But it'll not to call trace_block_plug.
>
> But call blk_flush_plug_list,it will trace_block_unplug all request_queue.
ok, this is true. please send a new patch for the item 1&2 then.
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