Re: [PATCH v3] btrfs: introduce offload_csum_mode to tweak checksum offloading behavior

[David Sterba <dsterba@suse.cz>]

On Mon, Feb 05, 2024 at 10:01:16PM +0900, Naohiro Aota wrote:
> We disable offloading checksum to workqueues and do it synchronously when
> the checksum algorithm is fast. However, as reported in the link below,
> RAID0 with multiple devices may suffer from the sync checksum, because
> "fast checksum" is still not fast enough to catch up RAID0 writing.
> 
> To measure the effectiveness of sync checksum and checksum offloading for
> developers, it would be better to have a switch for the checksum offloading
> under CONFIG_BTRFS_DEBUG hood.
> 
> This commit introduces fs_devices->offload_csum_mode for
> CONFIG_BTRFS_DEBUG, so that a btrfs developer can change the behavior by
> writing to /sys/fs/btrfs/<uuid>/offload_csum. The default is "auto" which
> is the same as the previous behavior. Or, you can set "on" or "off" (or "y"
> or "n" whatever kstrtobool() accepts) to always/never offload checksum.
> 
> More benchmark should be collected with this knob to implement a proper
> criteria to enable/disable checksum offloading.
> 
> Link: https://lore.kernel.org/linux-btrfs/20230731152223.4EFB.409509F4@e16-tech.com/
> Link: https://lore.kernel.org/linux-btrfs/p3vo3g7pqn664mhmdhlotu5dzcna6vjtcoc2hb2lsgo2fwct7k@xzaxclba5tae/
> Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>

I'm adding this to for-next.