On 01/07/2022 00:49, Damien Le Moal wrote:
+ if (dma_dev) {
+ shost->max_sectors = min_t(unsigned int, shost->max_sectors,
+ dma_opt_mapping_size(dma_dev) >> SECTOR_SHIFT);
+ }
Hi Damien,
> Hmm... shost->max_sectors becomes the max_hw_sectors limit for the block
> dev. So using dma_max_mapping_size(dma_dev) for that limit makes sense.
> Shouldn't dma_opt_mapping_size(dma_dev) be used to limit only the default
> "soft" limit (queue max_sectors limit) instead of the hard limit ?
>
Sure, it would sensible to use dma_opt_mapping_size() to limit the
default queue max sectors limit, while dma_max_mapping_size() limits the
host max sectors. But I didn't see in practice how limiting the shost
max sectors to dma_opt_mapping_size() makes a difference:
- block queue max_hw_sectors_kb file is read-only, so we cannot change
the queue max sectors from there
- And no SAS driver actually tries to modify upwards from the default.
I do note that USB storage driver as an example of a scsi driver which
does (modify from shost max sectors): see scsiglue.c::slave_configure()
Finally there is no common method to limit the default request queue max
sectors for those SAS drivers - I would need to add this limit in each
of their slave_configure callbacks, and I didn't think that its worth it.
Thanks,
John
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