From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx2.fusionio.com ([66.114.96.31]:60323 "EHLO mx2.fusionio.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751643Ab2GJS6Z (ORCPT ); Tue, 10 Jul 2012 14:58:25 -0400 Date: Tue, 10 Jul 2012 14:58:22 -0400 From: Josef Bacik To: Liu Bo CC: "linux-btrfs@vger.kernel.org" Subject: Re: [PATCH RFC] Btrfs: improve multi-thread buffer read Message-ID: <20120710185822.GE7529@localhost.localdomain> References: <1341919679-13792-1-git-send-email-liubo2009@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" In-Reply-To: <1341919679-13792-1-git-send-email-liubo2009@cn.fujitsu.com> Sender: linux-btrfs-owner@vger.kernel.org List-ID: On Tue, Jul 10, 2012 at 05:27:59AM -0600, Liu Bo wrote: > While testing with my buffer read fio jobs[1], I find that btrfs does not > perform well enough. > > Here is a scenario in fio jobs: > > We have 4 threads, "t1 t2 t3 t4", starting to buffer read a same file, > and all of them will race on add_to_page_cache_lru(), and if one thread > successfully puts its page into the page cache, it takes the responsibility > to read the page's data. > > And what's more, reading a page needs a period of time to finish, in which > other threads can slide in and process rest pages: > > t1 t2 t3 t4 > add Page1 > read Page1 add Page2 > | read Page2 add Page3 > | | read Page3 add Page4 > | | | read Page4 > -----|------------|-----------|-----------|-------- > v v v v > bio bio bio bio > > Now we have four bios, each of which holds only one page since we need to > maintain consecutive pages in bio. Thus, we can end up with far more bios > than we need. > > Here we're going to > a) delay the real read-page section and > b) try to put more pages into page cache. > > With that said, we can make each bio hold more pages and reduce the number > of bios we need. > > Here is some numbers taken from fio results: > w/o patch w patch > ------------- -------- --------------- > READ: 745MB/s +32% 987MB/s > Um, I have this in btrfs-next Btrfs: use large extent range for read and its endio that seems to do the same thing, did you not want to do that anymore? Thanks, Josef