Re: [PATCH net-next v2 2/2] net: ovs: use CRC32 accelerated flow hash if available

On Fri, Dec 13, 2013 at 1:55 AM, Francesco Fusco [off-list ref] wrote:

On 12/12/2013 09:20 PM, Jesse Gross wrote:

quoted

Out of curiosity, did you try using crc32q? OVS data structures are
already aligned to 8 bytes. It would also be interesting to know if a
parallelized implementation is worthwhile, although my guess is that
the OVS flow key is not quite long enough.

We did not try with crc32q yet because we had the very same concerns.
In the general case, when the length of the key is not a multiple of 8
bytes, we will have to use the crc32q to process multiple 64 bit numbers,
then process the the rest with a crc32l. My guess is that the
performance benefit won't be that high.

On 64-bit platforms, OVS already enforces alignment and multiples of 8
bytes for flow keys. If we introduced a hash primitive that does 8
bytes at a time instead of 4, there should be nothing extra to process
(although I don't know how big the upside would be).