On 09/08/2022 10:58, John Garry wrote:
commit: 0568e6122574dcc1aded2979cd0245038efe22b6 ("ata: libata-scsi:
cap ata_device->max_sectors according to shost->max_sectors")
https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git master
in testcase: stress-ng
on test machine: 96 threads 2 sockets Ice Lake with 256G memory
with following parameters:
nr_threads: 10%
disk: 1HDD
testtime: 60s
fs: f2fs
class: filesystem
test: copy-file
cpufreq_governor: performance
ucode: 0xb000280
Without knowing what the device adapter is, hard to say where the
problem is. I
suspect that with the patch applied, we may be ending up with a small
default
max_sectors value, causing overhead due to more commands than necessary.
Will check what I see with my test rig.
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.
thanks,
John
