Re: [RFC 0/8] Reliably generate large request from SRP

Or Gerlitz
2011-01-24T15:32:04Z

David Dillow wrote:
>> if we look on the 50% for SAS/1M IOs that you're presenting, can you tell
>> what made the difference, srp went from sg_tablesize of 255 to 256 so the
>> upper layers where able to provide 1M as one IO

> This win is from sg_tablesize going from 255 to 256 in this case; the HW
> really likes that better than getting two requests -- one for 1020 KB
> and one for 4 KB.

Its always nice to find the simplest explanation to the greatest improvement... going to the 2nd largest gains

> SAS 2M 520 MB/s 861 MB/s
> SAS 4M 529 MB/s 921 MB/s
> SAS 8M 600 MB/s 951 MB/s

I wonder what made the difference here? it can't be only the 255 --> 256 sg_tablesize change, for the 2M case the change to use 512 pages FMRs could let you use one rkey/fmr for the whole IO but not for 4M/8M

Or.