linux-kernel - Re: very low IOPS due to "block: reduce kblockd_mod_delayed_work

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Message-ID: <7d1e4bb8-1a73-9529-3191-66df4ff2d5fe@kernel.dk>
Date:   Sat, 18 Dec 2021 12:02:38 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     "Alex Xu (Hello71)" <alex_y_xu@...oo.ca>,
        linux-block@...r.kernel.org, Dexuan Cui <decui@...rosoft.com>,
        ming.lei@...hat.com, hch@....de, Long Li <longli@...rosoft.com>,
        "Michael Kelley (LINUX)" <mikelley@...rosoft.com>,
        linux-kernel@...r.kernel.org
Subject: Re: very low IOPS due to "block: reduce kblockd_mod_delayed_work_on()
 CPU consumption"

On 12/18/21 11:57 AM, Alex Xu (Hello71) wrote:
> Hi,
> 
> I recently noticed that between 6441998e2e and 9eaa88c703, I/O became 
> much slower on my machine using ext4 on dm-crypt on NVMe with bfq 
> scheduler. Checking iostat during heavy usage (find / -xdev and fstrim 
> -v /), maximum IOPS had fallen from ~10000 to ~100. Reverting cb2ac2912a 
> ("block: reduce kblockd_mod_delayed_work_on() CPU consumption") resolves 
> the issue.

Hmm interesting. I'll try and see if I can reproduce this and come up
with a fix.

-- 
Jens Axboe