On 12/08/2022 19:27, Damien Le Moal wrote:
Interestingly ata dev max_sectors kb also gets capped from 32MB (LBA48)
-> 256KB due to swiotlb max mapping size. (It would be capped by shost
default max sectors 512KB without that swiotlb limit). I assume capping
due to swiotlb limit is not occuring on Oliver's machine.
Yes, I was suspecting that we may be seeing a difference for anything that is
not AHCI, e.g. with other drivers.
But that seems to be the correct thing to do, no ?
Yes, this should be the correct thing to do.
> How was this working before
> without applying the swiotlb limit ?
>
Not sure. I would need to check the libata code for how it handles DMA
mapping errors, which I assume would occur for when we exceed the
swiotlb limit.
Having said this, from limited testing, whenever I check megaraid sas or
mpt3sas for performance, the length of request data never/rarely comes
close to max sectors. That why I am surprised with the regression which
Oliver reports.
Thanks,
John
