Re: [LKP] Re: [ext4] b1b4705d54: filebench.sum_bytes_mb/s -20.2% regression

From: Xing Zhengjun
Date: Wed Mar 04 2020 - 03:15:46 EST


Hi Matthew,

We test it in v5.6-rc4, the issue still exist, do you have time to take a look at this? Thanks.

On 1/8/2020 10:31 AM, Rong Chen wrote:


On 1/8/20 1:28 AM, Jan Kara wrote:
On Tue 07-01-20 11:57:08, Theodore Y. Ts'o wrote:
On Tue, Jan 07, 2020 at 02:41:06PM +0100, Jan Kara wrote:
Hello,

On Tue 24-12-19 08:59:15, kernel test robot wrote:
FYI, we noticed a -20.2% regression of filebench.sum_bytes_mb/s due to commit:


commit: b1b4705d54abedfd69dcdf42779c521aa1e0fbd3 ("ext4: introduce direct I/O read using iomap infrastructure")
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master

in testcase: filebench
on test machine: 8 threads Intel(R) Core(TM) i7-4770 CPU @ 3.40GHz with 8G memory
with following parameters:

ÂÂÂÂdisk: 1HDD
ÂÂÂÂfs: ext4
ÂÂÂÂtest: fivestreamreaddirect.f
ÂÂÂÂcpufreq_governor: performance
ÂÂÂÂucode: 0x27
I was trying to reproduce this but I failed with my test VM. I had SATA SSD
as a backing store though so maybe that's what makes a difference. Maybe
the new code results in somewhat more seeks because the five threads which
compete in submitting sequential IO end up being more interleaved?
A "-20.2% regression" should be read as a "20.2% performance
improvement" is zero-day kernel speak.
Are you sure? I can see:

ÂÂÂÂÂ 58.30 ÂÂ 2%ÂÂÂÂ -20.2%ÂÂÂÂÂ 46.53ÂÂÂÂÂÂÂ filebench.sum_bytes_mb/s

which implies to me previously the throughput was 58 MB/s and after the
commit it was 46 MB/s?

Anyway, in my testing that commit made no difference in that benchmark
whasoever (getting around 97 MB/s for each thread before and after the
commit).
ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ Honza

We're sorry for the misunderstanding, "-20.2%" means the change of filebench.sum_bytes_mb/s,
"regression" means the explanation of this change from LKP.

Best Regards,
Rong Chen
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--
Zhengjun Xing