lkml.org 
[lkml]   [2012]   [May]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [RESEND][PATCH v2] block: remove plugging at buffered write time
    On Thu, Apr 12, 2012 at 04:26:34PM +0200, Jan Kara wrote:
    > Hi Fengguang,
    >
    > On Thu 12-04-12 10:20:40, Wu Fengguang wrote:
    > > > > > > Note that plugging for O_SYNC writes is also removed. The user may pass
    > > > > > > arbitrary @size arguments, which may be much larger than the preferable
    > > > > > > I/O size, or may cross extent/device boundaries. Let the lower layers
    > > > > > > handle the plugging. Otherwise the plugging code here will turn the
    > > > > > > low level plugging into no-ops.
    > > > > >
    > > > > > I assume you have some numbers to back this up, right? Care to share
    > > > > > those?
    > > > >
    > > > > Yes please.
    > > > >
    > > > > We've broken this stuff a few times recently - we should review and
    > > > > test carefully.
    > > >
    > > > Yes sure. Last time I posted the patch, I did some tests and found no
    > > > performance changes. Now for 3.3, the tests started days ago have not
    > > > finished now (partly because it is stalled for quite long time due to
    > > > unknown reason). The now-available numbers for bs=4k dd's look fine.
    > > > The pending tests are for bs=1M dd's and some random fio workloads.
    > > >
    > >
    > > The changes are basically small enough to be considered noises.
    > > But anyway here are some interpretations:
    > >
    > > - application visible data write performance (write_bw) is almost the same
    > > - it slightly reduces the real IOs that hit disk (io_wkB_s, io_rkB_s)
    > > - disk utilization slightly increased
    > > - CPU time is slightly reduced
    > >
    > Well, two of the throughput numbers stand out (in both directions
    > actually) although they seem to be more extreme configurations so maybe it
    > is a noise. But maybe it would deserve further check:
    >
    > > $ ./compare-io bay/*/*-{3.3.0,3.3.0-plug+}
    > > 3.3.0 3.3.0-plug+
    > > ------------------------ ------------------------
    > ...
    > > 2.60 +7.1% 2.78 bay/thresh=1M/btrfs-10dd-1-3.3.0
    > > 3.72 -12.5% 3.25 bay/thresh=1M/btrfs-1dd-1-3.3.0

    For that btrfs performance bug, Yan Zheng helped me track down the
    root cause to be the hack in btree_writepages(), as we are discussing
    solutions to this in the other emails.

    > I looked at other iostat numbers as well, but seeing quite some changes
    > in both directions I'd say that those iostat numbers are too noisy to draw
    > serious conclusion from them.

    So let's proceed with the plugging change? I'll repost the split
    plugging patches.

    Thanks,
    Fengguang


    \
     
     \ /
      Last update: 2012-05-06 14:01    [W:0.027 / U:87.412 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site