Messages in this thread | | | Date | Tue, 29 Jul 2014 13:14:40 -0400 | From | Austin S Hemmelgarn <> | Subject | Re: Multi Core Support for compression in compression.c |
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On 2014-07-29 13:08, Nick Krause wrote: > On Mon, Jul 28, 2014 at 2:36 PM, Nick Krause <xerofoify@gmail.com> wrote: >> On Mon, Jul 28, 2014 at 12:19 PM, Austin S Hemmelgarn >> <ahferroin7@gmail.com> wrote: >>> On 2014-07-28 11:57, Nick Krause wrote: >>>> On Mon, Jul 28, 2014 at 11:13 AM, Nick Krause <xerofoify@gmail.com> >>>> wrote: >>>>> On Mon, Jul 28, 2014 at 6:10 AM, Austin S Hemmelgarn >>>>> <ahferroin7@gmail.com> wrote: >>>>>> On 07/27/2014 11:21 PM, Nick Krause wrote: >>>>>>> On Sun, Jul 27, 2014 at 10:56 PM, Austin S Hemmelgarn >>>>>>> <ahferroin7@gmail.com> 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 > It might be more work now, but it would probably be better in the long run to do it using kernel workqueues, as they would provide better support for suspend/hibernate/resume, and then you wouldn't need to worry about scheduling or how many CPU cores are in the system.
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