Re: [RESEND][PATCH v2] block: remove plugging at buffered write time

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On Wed, Apr 11, 2012 at 04:13:44PM -0700, Andrew Morton wrote:
> On Mon, 09 Apr 2012 10:34:44 -0400
> Jeff Moyer <jmoyer@xxxxxxxxxx> wrote:
> 
> > Wu Fengguang <fengguang.wu@xxxxxxxxx> writes:
> > 
> > > Buffered write(2) is not directly tied to IO, so it's not suitable to
> > > handle plug in generic_file_aio_write().
> > [snip, moved]
> > > 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.

$ ./compare bay/*/*-{3.3.0,3.3.0-plug+}
                   3.3.0               3.3.0-plug+
------------------------  ------------------------
                  196.94        -0.0%       196.86  bay/JBOD-2HDD-thresh=1000M/btrfs-10dd-1-3.3.0
                  196.67        +0.2%       196.99  bay/JBOD-2HDD-thresh=1000M/btrfs-1dd-1-3.3.0
                  134.34        -0.1%       134.26  bay/JBOD-2HDD-thresh=1000M/ext3-100dd-1-3.3.0
                  141.75        +0.1%       141.92  bay/JBOD-2HDD-thresh=1000M/ext3-10dd-1-3.3.0
                  166.74        +0.1%       166.89  bay/JBOD-2HDD-thresh=1000M/ext3-1dd-1-3.3.0
                  165.90        -0.1%       165.69  bay/JBOD-2HDD-thresh=1000M/ext4-100dd-1-3.3.0
                  186.83        +0.9%       188.60  bay/JBOD-2HDD-thresh=1000M/ext4-10dd-1-3.3.0
                  193.30        -0.1%       193.04  bay/JBOD-2HDD-thresh=1000M/ext4-1dd-1-3.3.0
                  168.34        +0.1%       168.48  bay/JBOD-2HDD-thresh=1000M/xfs-100dd-1-3.3.0
                  193.43        -0.3%       192.91  bay/JBOD-2HDD-thresh=1000M/xfs-10dd-1-3.3.0
                  197.59        -0.2%       197.14  bay/JBOD-2HDD-thresh=1000M/xfs-1dd-1-3.3.0
                  197.09        -0.1%       196.90  bay/JBOD-2HDD-thresh=100M/btrfs-10dd-1-3.3.0
                  197.20        +0.1%       197.48  bay/JBOD-2HDD-thresh=100M/btrfs-1dd-1-3.3.0
                  139.07        -0.6%       138.24  bay/JBOD-2HDD-thresh=100M/ext3-10dd-1-3.3.0
                  157.10        -0.1%       156.99  bay/JBOD-2HDD-thresh=100M/ext3-1dd-1-3.3.0
                  113.36        -0.6%       112.73  bay/JBOD-2HDD-thresh=100M/ext4-100dd-1-3.3.0
                  159.88        -0.5%       159.09  bay/JBOD-2HDD-thresh=100M/ext4-10dd-1-3.3.0
                  191.53        +0.3%       192.09  bay/JBOD-2HDD-thresh=100M/ext4-1dd-1-3.3.0
                   83.65        +0.4%        83.99  bay/JBOD-2HDD-thresh=100M/xfs-100dd-1-3.3.0
                  163.12        +0.3%       163.54  bay/JBOD-2HDD-thresh=100M/xfs-10dd-1-3.3.0
                  194.25        +0.3%       194.88  bay/JBOD-2HDD-thresh=100M/xfs-1dd-1-3.3.0
                  194.98        +0.2%       195.34  bay/RAID0-2HDD-thresh=1000M/btrfs-10dd-1-3.3.0
                  194.78        +0.1%       194.96  bay/RAID0-2HDD-thresh=1000M/btrfs-1dd-1-3.3.0
                  133.07        -0.1%       132.95  bay/RAID0-2HDD-thresh=1000M/ext3-10dd-1-3.3.0
                  136.90        -0.8%       135.82  bay/RAID0-2HDD-thresh=1000M/ext3-1dd-1-3.3.0
                  167.61        -1.2%       165.65  bay/RAID0-2HDD-thresh=1000M/ext4-100dd-1-3.3.0
                  188.04        +1.1%       190.10  bay/RAID0-2HDD-thresh=1000M/ext4-10dd-1-3.3.0
                  187.74        -0.3%       187.27  bay/RAID0-2HDD-thresh=1000M/ext4-1dd-1-3.3.0
                  169.01        +0.5%       169.80  bay/RAID0-2HDD-thresh=1000M/xfs-100dd-1-3.3.0
                  192.03        +0.0%       192.10  bay/RAID0-2HDD-thresh=1000M/xfs-10dd-1-3.3.0
                  196.06        +0.0%       196.14  bay/RAID0-2HDD-thresh=1000M/xfs-1dd-1-3.3.0
                  189.04        -0.6%       187.92  bay/RAID0-2HDD-thresh=100M/btrfs-10dd-1-3.3.0
                  183.23        -0.6%       182.05  bay/RAID0-2HDD-thresh=100M/btrfs-1dd-1-3.3.0
                  137.19        -0.1%       137.12  bay/RAID0-2HDD-thresh=100M/ext3-10dd-1-3.3.0
                  140.61        -0.1%       140.54  bay/RAID0-2HDD-thresh=100M/ext3-1dd-1-3.3.0
                  114.32        -2.3%       111.71  bay/RAID0-2HDD-thresh=100M/ext4-100dd-1-3.3.0
                  162.42        -0.1%       162.31  bay/RAID0-2HDD-thresh=100M/ext4-10dd-1-3.3.0
                  183.84        -0.9%       182.19  bay/RAID0-2HDD-thresh=100M/ext4-1dd-1-3.3.0
                   89.10        -0.3%        88.84  bay/RAID0-2HDD-thresh=100M/xfs-100dd-1-3.3.0
                  162.48        -0.2%       162.20  bay/RAID0-2HDD-thresh=100M/xfs-10dd-1-3.3.0
                  188.15        +0.5%       189.12  bay/RAID0-2HDD-thresh=100M/xfs-1dd-1-3.3.0
                   97.79        -0.0%        97.76  bay/RAID1-2HDD-thresh=1000M/btrfs-10dd-1-3.3.0
                   97.69        +0.0%        97.71  bay/RAID1-2HDD-thresh=1000M/btrfs-1dd-1-3.3.0
                   69.84        -1.1%        69.05  bay/RAID1-2HDD-thresh=1000M/ext3-10dd-1-3.3.0
                   76.62        -0.0%        76.59  bay/RAID1-2HDD-thresh=1000M/ext3-1dd-1-3.3.0
                   83.97        -0.0%        83.95  bay/RAID1-2HDD-thresh=1000M/ext4-100dd-1-3.3.0
                   94.87        -0.1%        94.79  bay/RAID1-2HDD-thresh=1000M/ext4-10dd-1-3.3.0
                   96.87        +0.6%        97.46  bay/RAID1-2HDD-thresh=1000M/ext4-1dd-1-3.3.0
                   84.57        -0.1%        84.50  bay/RAID1-2HDD-thresh=1000M/xfs-100dd-1-3.3.0
                   95.51        +0.2%        95.67  bay/RAID1-2HDD-thresh=1000M/xfs-10dd-1-3.3.0
                   97.44        -0.3%        97.12  bay/RAID1-2HDD-thresh=1000M/xfs-1dd-1-3.3.0
                   97.69        -0.1%        97.56  bay/RAID1-2HDD-thresh=100M/btrfs-10dd-1-3.3.0
                   97.75        +0.1%        97.87  bay/RAID1-2HDD-thresh=100M/btrfs-1dd-1-3.3.0
                   66.68        -0.3%        66.45  bay/RAID1-2HDD-thresh=100M/ext3-10dd-1-3.3.0
                   76.23        -0.7%        75.73  bay/RAID1-2HDD-thresh=100M/ext3-1dd-1-3.3.0
                   59.36        +0.9%        59.93  bay/RAID1-2HDD-thresh=100M/ext4-100dd-1-3.3.0
                   82.63        -0.1%        82.56  bay/RAID1-2HDD-thresh=100M/ext4-10dd-1-3.3.0
                   95.77        +0.1%        95.86  bay/RAID1-2HDD-thresh=100M/ext4-1dd-1-3.3.0
                   43.77        -0.1%        43.71  bay/RAID1-2HDD-thresh=100M/xfs-100dd-1-3.3.0
                   84.24        +0.3%        84.48  bay/RAID1-2HDD-thresh=100M/xfs-10dd-1-3.3.0
                   97.81        -0.1%        97.76  bay/RAID1-2HDD-thresh=100M/xfs-1dd-1-3.3.0
                   99.27        -0.0%        99.25  bay/thresh=1000M/btrfs-10dd-1-3.3.0
                   99.39        +0.0%        99.39  bay/thresh=1000M/btrfs-1dd-1-3.3.0
                   69.75        +0.2%        69.86  bay/thresh=1000M/ext3-100dd-1-3.3.0
                   71.79        -0.0%        71.76  bay/thresh=1000M/ext3-10dd-1-3.3.0
                   80.00        -0.0%        79.99  bay/thresh=1000M/ext3-1dd-1-3.3.0
                   89.38        -0.1%        89.30  bay/thresh=1000M/ext4-100dd-1-3.3.0
                   96.43        +0.2%        96.63  bay/thresh=1000M/ext4-10dd-1-3.3.0
                   98.57        -0.3%        98.28  bay/thresh=1000M/ext4-1dd-1-3.3.0
                   93.97        -0.2%        93.76  bay/thresh=1000M/xfs-100dd-1-3.3.0
                   97.51        +0.1%        97.57  bay/thresh=1000M/xfs-10dd-1-3.3.0
                   99.68        +0.1%        99.74  bay/thresh=1000M/xfs-1dd-1-3.3.0
                   97.82        -0.2%        97.64  bay/thresh=1000M:990M/btrfs-10dd-1-3.3.0
                   98.93        +0.7%        99.58  bay/thresh=1000M:990M/btrfs-1dd-1-3.3.0
                   69.60        -0.0%        69.58  bay/thresh=1000M:990M/ext3-100dd-1-3.3.0
                   72.97        -0.2%        72.83  bay/thresh=1000M:990M/ext3-10dd-1-3.3.0
                   79.76        +0.3%        79.99  bay/thresh=1000M:990M/ext3-1dd-1-3.3.0
                   90.58        -2.1%        88.70  bay/thresh=1000M:990M/ext4-100dd-1-3.3.0
                   95.27        -0.2%        95.06  bay/thresh=1000M:990M/ext4-10dd-1-3.3.0
                   96.91        +1.6%        98.48  bay/thresh=1000M:990M/ext4-1dd-1-3.3.0
                   93.79        -0.4%        93.41  bay/thresh=1000M:990M/xfs-100dd-1-3.3.0
                   97.07        -0.4%        96.70  bay/thresh=1000M:990M/xfs-10dd-1-3.3.0
                   99.09        -0.0%        99.04  bay/thresh=1000M:990M/xfs-1dd-1-3.3.0
                   96.28        -0.2%        96.06  bay/thresh=1000M:999M/btrfs-10dd-1-3.3.0
                   94.83        +1.4%        96.15  bay/thresh=1000M:999M/btrfs-1dd-1-3.3.0
                   69.70        +0.2%        69.81  bay/thresh=1000M:999M/ext3-100dd-1-3.3.0
                   72.79        -0.3%        72.55  bay/thresh=1000M:999M/ext3-10dd-1-3.3.0
                   79.75        -0.1%        79.69  bay/thresh=1000M:999M/ext3-1dd-1-3.3.0
                   87.95        +1.6%        89.38  bay/thresh=1000M:999M/ext4-100dd-1-3.3.0
                   95.18        +0.0%        95.20  bay/thresh=1000M:999M/ext4-10dd-1-3.3.0
                   98.58        -2.3%        96.36  bay/thresh=1000M:999M/ext4-1dd-1-3.3.0
                   92.54        -0.1%        92.46  bay/thresh=1000M:999M/xfs-100dd-1-3.3.0
                   96.81        -0.4%        96.42  bay/thresh=1000M:999M/xfs-10dd-1-3.3.0
                   99.29        -0.4%        98.91  bay/thresh=1000M:999M/xfs-1dd-1-3.3.0
                   99.03        +0.1%        99.13  bay/thresh=100M/btrfs-10dd-1-3.3.0
                   99.55        -0.1%        99.40  bay/thresh=100M/btrfs-1dd-1-3.3.0
                   55.68        -0.4%        55.48  bay/thresh=100M/ext3-100dd-1-3.3.0
                   71.40        -0.6%        70.95  bay/thresh=100M/ext3-10dd-1-3.3.0
                   79.82        +0.1%        79.88  bay/thresh=100M/ext3-1dd-1-3.3.0
                   63.21        -0.4%        62.99  bay/thresh=100M/ext4-100dd-1-3.3.0
                   84.42        +0.0%        84.45  bay/thresh=100M/ext4-10dd-1-3.3.0
                   95.65        +1.9%        97.44  bay/thresh=100M/ext4-1dd-1-3.3.0
                   49.61        +0.5%        49.87  bay/thresh=100M/xfs-100dd-1-3.3.0
                   87.76        -0.0%        87.76  bay/thresh=100M/xfs-10dd-1-3.3.0
                   99.34        +0.0%        99.36  bay/thresh=100M/xfs-1dd-1-3.3.0
                   92.98        -0.7%        92.29  bay/thresh=10M/btrfs-10dd-1-3.3.0
                   89.07        +0.4%        89.44  bay/thresh=10M/btrfs-1dd-1-3.3.0
                   61.76        +0.1%        61.80  bay/thresh=10M/ext3-10dd-1-3.3.0
                   75.72        +0.3%        75.96  bay/thresh=10M/ext3-1dd-1-3.3.0
                   67.89        -0.2%        67.77  bay/thresh=10M/ext4-10dd-1-3.3.0
                   92.00        -0.3%        91.73  bay/thresh=10M/ext4-1dd-1-3.3.0
                   69.71        -0.4%        69.45  bay/thresh=10M/xfs-10dd-1-3.3.0
                   92.23        +1.8%        93.89  bay/thresh=10M/xfs-1dd-1-3.3.0
                    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
                   62.41        +0.3%        62.60  bay/thresh=1M/ext3-10dd-1-3.3.0
                   58.61        +0.4%        58.82  bay/thresh=1M/ext3-1dd-1-3.3.0
                   70.70        -1.1%        69.92  bay/thresh=1M/ext4-10dd-1-3.3.0
                   84.81        +0.1%        84.90  bay/thresh=1M/ext4-1dd-1-3.3.0
                   66.05        -0.1%        65.97  bay/thresh=1M/xfs-10dd-1-3.3.0
                   74.81        +0.1%        74.85  bay/thresh=1M/xfs-1dd-1-3.3.0
                13467.55        -0.0%     13460.98  TOTAL write_bw

> > > Also moves unplugging for direct I/O from around ->direct_IO() down to
> > > do_blockdev_direct_IO().
> > 
> > This could be handled in a separate patch.
> 
> I think that would be better.

OK. I'll split it on next post, after the tests complete.

Thanks,
Fengguang
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