[Virtio-fs] [PATCH v4 0/2] virtiofsd: Improve io bandwidth by replacing pwrite with pwritev

[piaojun]

On 2019/8/11 10:06, Eric Ren wrote:
> Hi jun,
> 
> On Fri, Aug 09, 2019 at 08:50:12AM +0800, piaojun wrote:
>> >From my test, write bandwidth will be improved greatly by replacing
>> pwrite with pwritev, and the test result as below:
> 
> Could you share more information about this testing?
> 
> - args for qemu: cache size?
> - args for virtiofsd: which cache mode？
> - DAX is used, right?

DAX is disabled, as this optimization only works on Host side.

> 
> - which kind of disk are you using, what's then IOPS/BW limit?
> 
> I tried this patch with HDD disk - IOPS:5000, BW: 140MB/s.

I used EXT4 and ramdisk as backend device.

> 
> - VM: 4 vcpus, 8G mem
> - cache=always, cache-size=8G, DAX
> - fio job
> 
> ```
> [global]
> fsync=0
> name=virtiofs-test
> filename=fio-test
> directory=$mntdir   # share dir for test sitting on the disk
> rw=randwrite
> bs=4K

*bs* should be 1M for bandwidth test which makes writev works well.

> direct=1
> numjobs=1
> time_based=0
> 
> [file1]
> size=2G
> io_size=40M
> ioengine=libaio
> iodepth=128
> ```
> - without this patch
> 
> ```
> file1: (g=0): rw=randwrite, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) 4096B-4096B, ioengine=libaio, iodepth=128
> fio-3.1
> Starting 1 process
> 
> file1: (groupid=0, jobs=1): err= 0: pid=11: Sat Aug 10 11:33:29 2019
>   write: IOPS=985, BW=3942KiB/s (4037kB/s)(40.0MiB/10390msec)
> ```
> 
> - with this patch applied
> 
> ```
> file1: (g=0): rw=randwrite, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) 4096B-4096B, ioengine=libaio, iodepth=128
> fio-3.1
> Starting 1 process
> 
> file1: (groupid=0, jobs=1): err= 0: pid=10: Sat Aug 10 15:31:57 2019
>   write: IOPS=1056, BW=4224KiB/s (4326kB/s)(40.0MiB/9696msec)
> 
> ```
> 
> the number is even worse than 9pfs.

Please modify your testcase as mentioned above, and share your result
again. I'm glad to find out where the problem is.

Jun

> 
> Thanks,
> Eric
> 
>>
>> ---
>> pwrite:
>> # fio -direct=1 -time_based -iodepth=64 -rw=randwrite -ioengine=libaio -bs=1M -size=1G -numjob=16 -runtime=30 -group_reporting -name=file -filename=/mnt/virtiofs/file
>> file: (g=0): rw=randwrite, bs=1M-1M/1M-1M/1M-1M, ioengine=libaio, iodepth=64
>> ...
>> fio-2.13
>> Starting 16 processes
>> Jobs: 16 (f=16): [w(16)] [100.0% done] [0KB/886.0MB/0KB /s] [0/886/0 iops] [eta 00m:00s]
>> file: (groupid=0, jobs=16): err= 0: pid=5799: Tue Aug 6 18:48:26 2019
>> write: io=26881MB, bw=916988KB/s, iops=895, runt= 30018msec
>>
>> pwritev:
>> # fio -direct=1 -time_based -iodepth=64 -rw=randwrite -ioengine=libaio -bs=1M -size=1G -numjob=16 -runtime=30 -group_reporting -name=file -filename=/mnt/virtiofs/file
>> file: (g=0): rw=randwrite, bs=1M-1M/1M-1M/1M-1M, ioengine=libaio, iodepth=64
>> ...
>> fio-2.13
>> Starting 16 processes
>> Jobs: 16 (f=16): [w(16)] [100.0% done] [0KB/1793MB/0KB /s] [0/1793/0 iops] [eta 00m:00s]
>> file: (groupid=0, jobs=16): err= 0: pid=6328: Tue Aug 6 18:22:17 2019
>> write: io=52775MB, bw=1758.7MB/s, iops=1758, runt= 30009msec
>> ---
>>
>> This patch introduces writev and pwritev for lo_write_buf(). I tried my
>> best not doing harm to the origin code construct, and there will be
>> some *useless* branches in fuse_buf_copy_one() which are hard to judge
>> if they will be useful in the future. So I just leave them alone
>> safely. If the cleanup work is necessary, please let me know.
>>
>> v2
>>   - Split into two patches
>>   - Add the lost flags support, such as FUSE_BUF_PHYS_ADDR
>>
>> v3
>>   - use git send-email to make the patch set in one thread
>>   - move fuse_buf_writev() into fuse_buf_copy()
>>   - use writev for the src buffers when they're alread already mapped by the daemon process
>>   - use calloc to replace malloc
>>   - set res 0 if writev() returns 0
>>
>> v4
>>   - iterate from in_buf->buf[0] rather than buf[1]
>>   - optimize the code to make it more elegant
>>
>> Jun Piao (2):
>>   add definition of fuse_buf_writev().
>>   use fuse_buf_writev to replace fuse_buf_write for better performance
>>
>> Signed-off-by: Jun Piao <piaojun at huawei.com>
>> Suggested-by: Dr. David Alan Gilbert <dgilbert at redhat.com>
>> Suggested-by: Stefan Hajnoczi <stefanha at redhat.com>
>> ---
>>  buffer.c      |   48 ++++++++++++++++++++++++++++++++++++++++++++++++
>>  fuse_common.h |   14 ++++++++++++++
>>  seccomp.c     |    2 ++
>>  3 files changed, 64 insertions(+)
>> --
>>
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> .
>