linux-kernel - Re: [PATCH 1/5] Btrfs: stop using btrfs_schedule

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Message-ID: <4b4664f4-2f49-bc4b-bc29-be10fb19a3a2@suse.com>
Date:   Thu, 11 Jul 2019 14:32:20 +0300
From:   Nikolay Borisov <nborisov@...e.com>
To:     Tejun Heo <tj@...nel.org>, clm@...com,
        David Sterba <dsterba@...e.com>, josef@...icpanda.com
Cc:     kernel-team@...com, axboe@...nel.dk, jack@...e.cz,
        linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] Btrfs: stop using btrfs_schedule_bio()



On 10.07.19 г. 22:28 ч., Tejun Heo wrote:
> From: Chris Mason <clm@...com>
> 
> btrfs_schedule_bio() hands IO off to a helper thread to do the actual
> submit_bio() call.  This has been used to make sure async crc and
> compression helpers don't get stuck on IO submission.  To maintain good
> performance, over time the IO submission threads duplicated some IO
> scheduler characteristics such as high and low priority IOs and they
> also made some ugly assumptions about request allocation batch sizes.
> 
> All of this cost at least one extra context switch during IO submission,
> and doesn't fit well with the modern blkmq IO stack.  So, this commit stops
> using btrfs_schedule_bio().  We may need to adjust the number of async
> helper threads for crcs and compression, but long term it's a better
> path.
> 
> Signed-off-by: Chris Mason <clm@...com>
> Reviewed-by: Josef Bacik <josef@...icpanda.com>

Reviewed-by: Nikolay Borisov <nborisov@...e.com>

<snip>