Messages in this thread | | | Date | Wed, 10 Aug 2022 09:33:23 +0100 | Subject | Re: [ata] 0568e61225: stress-ng.copy-file.ops_per_sec -15.0% regression | From | John Garry <> |
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On 09/08/2022 15:57, Damien Le Moal wrote: >>> As far as I can see, this patch should not make a difference unless the >>> ATA shost driver is setting the max_sectors value unnecessarily low. >> For __ATA_BASE_SHT, we don't set max_sectors. As such, we default >> shost->max_sectors = SCSI_DEFAULT_MAX_SECTORS (=1024) in >> scsi_host_alloc(). I assume no shost dma mapping limit applied. >> >> Then - for example - we could select dev->max_sectors = >> ATA_MAX_SECTORS_LBA48 (=65535) in ata_dev_configure(). >> >> So with commit 0568e6122574 we would have final max sectors = 1024, as >> opposed to 65535 previously. I guess that the problem is something like >> this. >> >> If so, it seems that we would need to apply the shost dma mapping limit >> separately in ata_scsi_dev_config() and not use shost->max_sectors. > OK. Will have a look at that. >
We may need to introduce something like shost->max_hw_sectors, which is set according to sht max sectors and dma mapping limits. That could be also used in USB scsiglue slave_configure()
Or else set max_sectors value for __ATA_BASE_SHT, but I don't know a sane value there considering ATA_MAX_SECTORS_LBA48 gives max_sectors of 65535.
Damien, please let me know if you need help now. I am just waiting for you to test to prove this theory about dev->max_sectors being capped. I don't have an AHCI setup readily-available for testing - just SAS cards or QEMU.
Thanks, John
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