linux-kernel - Re: [ext4] b1b4705d54: filebench.sum_bytes

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Date:   Tue, 7 Jan 2020 14:41:06 +0100
From:   Jan Kara <jack@...e.cz>
To:     kernel test robot <rong.a.chen@...el.com>
Cc:     Matthew Bobrowski <mbobrowski@...browski.org>,
        Theodore Ts'o <tytso@....edu>, Jan Kara <jack@...e.cz>,
        Ritesh Harjani <riteshh@...ux.ibm.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        lkp@...ts.01.org
Subject: Re: [ext4] b1b4705d54: filebench.sum_bytes_mb/s -20.2% regression

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:
> 
> 	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?

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR