Re: [PATCH v3 2/2] scsi: sd: Set a default optimal IO size if one is not defined

[Bart Van Assche <bvanassche@acm.org>]

On 6/11/25 11:02 PM, Damien Le Moal wrote:
> Introduce the helper function sd_set_io_opt() to set a disk io_opt
> limit. This new way of setting this limit falls back to using the
> max_sectors limit if the host does not define an optimal sector limit
> and the device did not indicate an optimal transfer size (e.g. as is
> the case for ATA devices). io_opt calculation is done using a local
> 64-bits variable to avoid overflows. The final value is clamped to
> UINT_MAX aligned down to the device physical block size.
> 
> This fallback io_opt limit avoids setting up the disk with a zero
> io_opt limit, which result in the rather small 128 KB read_ahead_kb
> attribute. The larger read_ahead_kb value set with the default non-zero
> io_opt limit significantly improves buffered read performance with file
> systems without any intervention from the user.
Reviewed-by: Bart Van Assche <bvanassche@acm.org>