Hi Jeff, Thank you for your comment.
On 05/09/2014 05:39 PM, Shaw, Jeffrey B wrote: > have you tested this patch to see if there is a negative impact to > performance? Yes, but not with testpmd. I passed our internal non-regression performance tests and it shows no difference (or below the error margin), even with low overhead processing like forwarding whatever the number of cores I use. > Wouldn't the processor have to mask the high bytes of the physical > address when it is used, for example, to populate descriptors with > buffer addresses? When compute bound, this could steal CPU cycles > away from packet processing. I think we should understand the > performance trade-off in order to save these 2 bytes. I would naively say that the cost is negligible: accessing to the length is the same as before (it's a 16 bits field) and accessing the physical address is just a mask or a shift, which should not be very long on an Intel processor (1 cycle?). This is to be compared with the number of cycles per packet in io-fwd mode, which is probably around 150 or 200. > It would be interesting to see how throughput is impacted when the > workload is core-bound. This could be accomplished by running testpmd > in io-fwd mode across 4x 10G ports. I agree, this is something we could check. If you agree, let's first wait for some other comments and see if we find a consensus on the patches. Regards, Olivier
