From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cn.fujitsu.com ([222.73.24.84]:40250 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1753901Ab2GKMxX (ORCPT ); Wed, 11 Jul 2012 08:53:23 -0400 Message-ID: <4FFD79D3.4090901@cn.fujitsu.com> Date: Wed, 11 Jul 2012 21:04:19 +0800 From: Liu Bo MIME-Version: 1.0 To: Josef Bacik CC: "linux-btrfs@vger.kernel.org" Subject: Re: [PATCH RFC] Btrfs: improve multi-thread buffer read References: <1341919679-13792-1-git-send-email-liubo2009@cn.fujitsu.com> <20120710185822.GE7529@localhost.localdomain> <4FFCDDA3.4000002@cn.fujitsu.com> <20120711123147.GH7529@localhost.localdomain> In-Reply-To: <20120711123147.GH7529@localhost.localdomain> Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-btrfs-owner@vger.kernel.org List-ID: On 07/11/2012 08:31 PM, Josef Bacik wrote: > On Tue, Jul 10, 2012 at 07:57:55PM -0600, Liu Bo wrote: >> On 07/11/2012 02:58 AM, Josef Bacik wrote: >> >>> 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, >>> >> >> >> I'm still hard working on that patchset. :) >> >> Although the patchset is well worthy of testing, it is not good enough for btrfs upstream. >> >> While doing some tuning work on it, I realized that I could make this improvement without >> the help of rwlock extent state stuff, so I made this smaller and cleaner patch for upstream >> so that we could gain some performance here first. >> > > So do you want me to drop the rwlock stuff and take this instead? Take a look > at whats in btrfs-next and tell me what I should drop. Thanks, > Yes Josef, please take this patch instead and drop the following: Btrfs: use radix tree for checksum Btrfs: merge adjacent states as much as possible Btrfs: use large extent range for read and its endio Btrfs: apply rwlock for extent state When I finish fixing all the noticed bugs on hands, I'll send a new rebased version to btrfs-next for you. :) thanks, liubo > Josef >