Messages in this thread | | | Date | Sat, 13 Aug 2022 08:23:36 +0100 | Subject | Re: [ata] 0568e61225: stress-ng.copy-file.ops_per_sec -15.0% regression | From | John Garry <> |
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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
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