linux-kernel - Re: [RFC PATCH] block:Fix some problems about handling plug in blk_queue

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Message-ID: <CANejiEXdHaqtXuR47QRimRNcvjxtUn8__7MK5XwW2t658hz=3g@mail.gmail.com>
Date:	Wed, 8 Aug 2012 11:06:34 +0800
From:	Shaohua Li <shli@...nel.org>
To:	Jianpeng Ma <majianpeng@...il.com>
Cc:	axboe <axboe@...nel.dk>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] block:Fix some problems about handling plug in blk_queue_bio().

2012/8/8 Jianpeng Ma <majianpeng@...il.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.

> 2:Only two device can trace plug.
I didn't get the point, can you have more details?

> 3:When exec blk_flush_plug_list,it use list_sort which has
> O(nlog(n)) complexity. When insert and sort, it only O(n) complexity.
but now you do the list iterator for every request, so it's O(n*n)?
The plug list is unlikely too long, so I didn't worry about the time
spending on list sort.
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