RE: [ata] 0568e61225: stress-ng.copy-file.ops_per_sec -15.0% regression

[David Laight]

...
> >> 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.
> 
> That is my hunch too, hence my question about which host driver is being used
> for this test... That is not apparent from the problem report.

No one's fallen over the old problem and managed to limit
the number of sectors in a read to the number of sectors
in (IIRC) a 'multi sector' read that uses a single DMA burst?

Was always a good way of killing disk performance.

IIRC the maximum number of sectors for an ATA disk transfer is 255.

	David

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