On 01/22/2016 07:14 AM, li.ping...@zte.com.cn wrote:
Hi Pranith, it is appreciated for your reply.
Pranith Kumar Karampuri <pkara...@redhat.com> 写于 2016/01/20 18:51:19:
> 发件人: Pranith Kumar Karampuri <pkara...@redhat.com>
> 收件人: li.ping...@zte.com.cn, gluster-devel@gluster.org,
> 日期: 2016/01/20 18:51
> 主题: Re: [Gluster-devel] Gluster AFR volume write performance has
> been seriously affected by GLUSTERFS_WRITE_IS_APPEND in afr_writev
>
> Sorry for the delay in response.
> On 01/15/2016 02:34 PM, li.ping...@zte.com.cn wrote:
> GLUSTERFS_WRITE_IS_APPEND Setting in afr_writev function at
> glusterfs client end makes the posix_writev in the server end deal
> IO write fops from parallel to serial in consequence.
>
> i.e. multiple io-worker threads carrying out IO write fops are
> blocked in posix_writev to execute final write fop pwrite/pwritev in
> __posix_writev function ONE AFTER ANOTHER.
>
> For example:
>
> thread1: iot_worker -> ... -> posix_writev() |
> thread2: iot_worker -> ... -> posix_writev() |
> thread3: iot_worker -> ... -> posix_writev() -> __posix_writev()
> thread4: iot_worker -> ... -> posix_writev() |
>
> there are 4 iot_worker thread doing the 128KB IO write fops as
> above, but only one can execute __posix_writev function and the
> others have to wait.
>
> however, if the afr volume is configured on with storage.linux-aio
> which is off in default, the iot_worker will use posix_aio_writev
> instead of posix_writev to write data.
> the posix_aio_writev function won't be affected by
> GLUSTERFS_WRITE_IS_APPEND, and the AFR volume write performance goes
up.
> I think this is a bug :-(.
Yeah, I agree with you. I suppose the GLUSTERFS_WRITE_IS_APPEND is a
misuse in afr_writev.
I checked the original intent of GLUSTERS_WRITE_IS_APPEND change at
review website:
_http://review.gluster.org/#/c/5501/_
The initial purpose seems to avoid an unnecessary fsync()in
afr_changelog_post_op_safe function if the writing data position
was currently at the end of the file, detected by
(preop.ia_size == offset || (fd->flags & O_APPEND)) in posix_writev.
In comparison with the afr write performance loss, I think
it costs too much.
I suggest to make the GLUSTERS_WRITE_IS_APPEND setting configurable
just as ensure-durability in afr.
You are right, it doesn't make sense to put this option in dictionary if
ensure-durability is off. http://review.gluster.org/13285 addresses
this. Do you want to try this out?
Thanks for doing most of the work :-). Do let me know if you want to
raise a bug for this. Or I can take that up if you don't have time.
Pranith
>
> So, my question is whether AFR volume could work fine with
> storage.linux-aio configuration which bypass the
> GLUSTERFS_WRITE_IS_APPEND setting in afr_writev,
> and why glusterfs keeps posix_aio_writev different from posix_writev ?
>
> Any replies to clear my confusion would be grateful, and thanks in
advance.
> What is the workload you have? multiple writers on same file workloads?
I test the afr gluster volume by fio like this:
fio --filename=/mnt/afr/20G.dat --direct=1 --rw=write --bs=128k
--size=20G --numjobs=8
--runtime=60 --group_reporting --name=afr_test --iodepth=1
--ioengine=libaio
The Glusterfs BRICKS are two IBM X3550 M3.
The local disk direct write performance of 128KB IO req block size is
about 18MB/s
in single thread and 80MB/s in 8 multi-threads.
If the GLUSTERS_WRITE_IS_APPEND is configed, the afr gluster volume
write performance is 18MB/s
as the single thread, and if not, the performance is nearby
75MB/s.(network bandwith is enough)
>
> Pranith
>
>
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