[Virtio-fs] [QUESTION] A performance problem for buffer write compared with 9p

[wangyan]

On 2019/8/22 19:43, Miklos Szeredi wrote:
> On Thu, Aug 22, 2019 at 2:59 AM wangyan <wangyan122 at huawei.com> wrote:
>> I will test it when I get the patch, and post the compared result with
>> 9p.
>
> Could you please try the attached patch?  My guess is that it should
> improve the performance, perhaps by a big margin.
>
> Further improvement is possible by eliminating page copies, but that
> is less trivial.
>
> Thanks,
> Miklos
>
Using the same test model. And the test result is:
	1. Latency
		virtiofs: avg-lat is 15.40 usec, bigger than before(6.64 usec).
		4K: (g=0): rw=write, bs=4K-4K/4K-4K/4K-4K, ioengine=psync, iodepth=1
		fio-2.13
		Starting 1 process
		Jobs: 1 (f=1): [W(1)] [100.0% done] [0KB/142.4MB/0KB /s] [0/36.5K/0 
iops] [eta 00m:00s]
		4K: (groupid=0, jobs=1): err= 0: pid=5528: Thu Aug 22 20:39:07 2019
		  write: io=6633.2MB, bw=226404KB/s, iops=56600, runt= 30001msec
			clat (usec): min=2, max=40403, avg=14.77, stdev=33.71
			 lat (usec): min=3, max=40404, avg=15.40, stdev=33.74

	2. Bandwidth
		virtiofs: bandwidth is 280840KB/s, lower than before(691894KB/s).
		1M: (g=0): rw=write, bs=1M-1M/1M-1M/1M-1M, ioengine=psync, iodepth=1
		fio-2.13
		Starting 1 process
		Jobs: 1 (f=1): [f(1)] [100.0% done] [0KB/29755KB/0KB /s] [0/29/0 iops] 
[eta 00m:00s]
		1M: (groupid=0, jobs=1): err= 0: pid=5550: Thu Aug 22 20:41:28 2019
		  write: io=8228.0MB, bw=280840KB/s, iops=274, runt= 30001msec
			clat (usec): min=362, max=11038, avg=3571.33, stdev=1062.72
			 lat (usec): min=411, max=11093, avg=3628.39, stdev=1064.53

According to the result, the patch doesn't work and make it worse than 
before.