Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753605AbaG2RIZ (ORCPT ); Tue, 29 Jul 2014 13:08:25 -0400 Received: from mail-vc0-f169.google.com ([209.85.220.169]:39507 "EHLO mail-vc0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750857AbaG2RIX (ORCPT ); Tue, 29 Jul 2014 13:08:23 -0400 MIME-Version: 1.0 In-Reply-To: References: <53D5BBCA.3020109@gmail.com> <53D6218A.5080401@gmail.com> <53D67828.3040802@gmail.com> Date: Tue, 29 Jul 2014 13:08:22 -0400 Message-ID: Subject: Re: Multi Core Support for compression in compression.c From: Nick Krause To: Austin S Hemmelgarn Cc: "linux-kernel@vger.kernel.org" , "linux-btrfs@vger.kernel.org SYSTEM list:BTRFS FILE" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 28, 2014 at 2:36 PM, Nick Krause wrote: > On Mon, Jul 28, 2014 at 12:19 PM, Austin S Hemmelgarn > wrote: >> On 2014-07-28 11:57, Nick Krause wrote: >>> On Mon, Jul 28, 2014 at 11:13 AM, Nick Krause >>> wrote: >>>> On Mon, Jul 28, 2014 at 6:10 AM, Austin S Hemmelgarn >>>> wrote: >>>>> On 07/27/2014 11:21 PM, Nick Krause wrote: >>>>>> On Sun, Jul 27, 2014 at 10:56 PM, Austin S Hemmelgarn >>>>>> wrote: >>>>>>> On 07/27/2014 04:47 PM, Nick Krause wrote: >>>>>>>> This may be a bad idea , but compression in brtfs seems >>>>>>>> to be only using one core to compress. Depending on the >>>>>>>> CPU used and the amount of cores in the CPU we can make >>>>>>>> this much faster with multiple cores. This seems bad by >>>>>>>> my reading at least I would recommend for writing >>>>>>>> compression we write a function to use a certain amount >>>>>>>> of cores based on the load of the system's CPU not using >>>>>>>> more then 75% of the system's CPU resources as my system >>>>>>>> when idle has never needed more then one core of my i5 >>>>>>>> 2500k to run when with interrupts for opening eclipse are >>>>>>>> running. For reading compression on good core seems fine >>>>>>>> to me as testing other compression software for reads , >>>>>>>> it's way less CPU intensive. Cheers Nick >>>>>>> We would probably get a bigger benefit from taking an >>>>>>> approach like SquashFS has recently added, that is, >>>>>>> allowing multi-threaded decompression fro reads, and >>>>>>> decompressing directly into the pagecache. Such an approach >>>>>>> would likely make zlib compression much more scalable on >>>>>>> large systems. >>>>>>> >>>>>>> >>>>>> >>>>>> Austin, That seems better then my idea as you seem to be more >>>>>> up to date on brtfs devolopment. If you and the other >>>>>> developers of brtfs are interested in adding this as a >>>>>> feature please let me known as I would like to help improve >>>>>> brtfs as the file system as an idea is great just seems like >>>>>> it needs a lot of work :). Nick >>>>> I wouldn't say that I am a BTRFS developer (power user maybe?), >>>>> but I would definitely say that parallelizing compression on >>>>> writes would be a good idea too (especially for things like >>>>> lz4, which IIRC is either in 3.16 or in the queue for 3.17). >>>>> Both options would be a lot of work, but almost any performance >>>>> optimization would. I would almost say that it would provide a >>>>> bigger performance improvement to get BTRFS to intelligently >>>>> stripe reads and writes (at the moment, any given worker thread >>>>> only dispatches one write or read to a single device at a >>>>> time, and any given write() or read() syscall gets handled by >>>>> only one worker). >>>>> >>>> >>>> I will look into this idea and see if I can do this for writes. >>>> Regards Nick >>> >>> Austin, Seems since we don't want to release the cache for inodes >>> in order to improve writes if are going to use the page cache. We >>> seem to be doing this for writes in end_compressed_bio_write for >>> standard pages and in end_compressed_bio_write. If we want to cache >>> write pages why are we removing then ? Seems like this needs to be >>> removed in order to start off. Regards Nick >>> >> I'm not entirely sure, it's been a while since I went exploring in the >> page-cache code. My guess is that there is some reason that you and I >> aren't seeing that we are trying for write-around semantics, maybe one >> of the people who originally wrote this code could weigh in? Part of >> this might be to do with the fact that normal page-cache semantics >> don't always work as expected with COW filesystems (cause a write goes >> to a different block on the device than a read before the write would >> have gone to). It might be easier to parallelize reads first, and >> then work from that (and most workloads would probably benefit more >> from the parallelized reads). >> > I will look into this later today and work on it then. > Regards Nick Seems the best way to do is to create a kernel thread per core like in NFS and depending on the load of the system use these threads. Regards Nick -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/