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

From: Jan Kara
Date: Tue Jan 07 2020 - 08:41:11 EST


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")
> master
> in testcase: filebench
> on test machine: 8 threads Intel(R) Core(TM) i7-4770 CPU @ 3.40GHz with 8G memory
> with following parameters:
> disk: 1HDD
> fs: ext4
> test: fivestreamreaddirect.f
> cpufreq_governor: performance
> ucode: 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?

Jan Kara <jack@xxxxxxxx>