lkml.org 
[lkml]   [2009]   [Feb]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    SubjectRe: Commit 31a12666d8f0c22235297e1c1575f82061480029 slows down Berkeley DB
    Date
    On Tuesday 03 February 2009 12:54:26 Zhang, Yanmin wrote:
    > On Tue, 2009-02-03 at 12:24 +1100, Nick Piggin wrote:
    > > On Friday 30 January 2009 12:23:15 Jan Kara wrote:
    > > > Hi,
    > > >
    > > > today I found that commit 31a12666d8f0c22235297e1c1575f82061480029
    > > > (mm: write_cache_pages cyclic fix) slows down operations over Berkeley
    > > > DB. Without this "fix", I can add 100k entries in about 5 minutes 30s,
    > > > with that change it takes about 20 minutes.
    > > > What is IMO happening is that previously we scanned to the end of
    > > > file, we left writeback_index at the end of file and went to write next
    > > > file. With the fix, we wrap around (seek) and after writing some more
    > > > we go to next file (seek again).
    >
    > We also found this commit causes about 40~50% regression with iozone
    > mmap-rand-write. #iozone -B -r 4k -s 64k -s 512m -s 1200m
    >
    > My machine has 8GB memory.

    Ah, thanks. Yes BDB I believe is basically just doing an mmap-rand-write,
    so maybe this is a good test case.

    The interesting thing is why is this causing such a slowdown. If there is
    only a single main file active in the workload, then I don't see why this
    patch should make such a big difference. In either case, wouldn't pdflush
    come back and just start writing out from the start of the file anyway?



    \
     
     \ /
      Last update: 2009-02-03 03:13    [W:3.979 / U:0.004 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site