Re: [patch 0/1] Apply segment size and segment boundary to integrity data

[Martin K. Petersen]

>>>>> "Christof" == Christof Schmitt <christof.schmitt@xxxxxxxxxx> writes:

Christof> To have a simple approach that covers the case with one
Christof> integrity data segment per user data segment, we only report
Christof> half the size for the scatterlist length when running
Christof> DIX. This guarantees that the other half can be used for
Christof> integrity data.

Yup, a few of our partners did something similar.

My concern is the scenario where we submit lots of 512-byte writes that
get merged into (in your case) 4 KB segments.  Each of those 512-byte
writes could come with an 8-byte integrity metadata tuple.  And so you'd
need 8 DI scatterlist elements per data element.


Christof> Meaning the integrity data sg list would have more entries
Christof> than max_segments? I have not seen this during my experiments,
Christof> but then i likely have not hit every case of a possible
Christof> request layout.

dd to the block device is usually a good way to issue long scatterlists.


Christof> Ok, i have to look into that as well. It would be an issue
Christof> with the approach we are looking at now: If there are
Christof> max_segments data segments, and more than max_segments
Christof> integrity data segments, we will overrun the hardware
Christof> constraint.

Ok.

-- 
Martin K. Petersen	Oracle Linux Engineering
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/