On 26/01/2016 08:23, "Ben Pfaff" <b...@ovn.org> wrote:
>On Tue, Jan 26, 2016 at 03:28:47AM +0000, Daniele Di Proietto wrote: >> >> >> On 25/01/2016 18:20, "Andy Zhou" <az...@ovn.org> wrote: >> >> >On Sun, Jan 24, 2016 at 8:32 AM, Ben Pfaff <b...@ovn.org> wrote: >> > >> >> Before this commit, emc_processing() copied a netdev_flow_key if >>there >> >>was >> >> no exact-match cache (EMC) hit. This commit eliminates the copy by >> >> constructing the netdev_flow_key in the place it would be copied. >> >> >> >> Found by inspection. >> >> >> >> Shahbaz (CCed) reports that this reduces the cost of an EMC miss by >>72 >> >> cycles in his test case in which the EMC is disabled. Presumably >>this >> >> is similarly valuable in cases where the EMC merely has few hits. >> >> >> >> CC: Muhammad Shahbaz <mshah...@cs.princeton.edu> >> >> Signed-off-by: Ben Pfaff <b...@ovn.org> >> >> >> > >> >Logic looks good to me. >> > >> >Acked-by: Andy Zhou <az...@ovn.org> >> > >> >I think Daniele is testing on performance impact on this patch. so it >>is >> >may be worthwhile >> >to wait for his input before pushing the change. >> >> If I disable the EMC I observe an increase in throughput when this patch >> is applied (from ~4.8 Mpps to ~5.4 Mpps). >> >> If the EMC is enabled, instead, I see a drop in throughput >> (from ~12.4 Mpps to ~12.0 Mpps) with this patch. >> >> At a first glance it looks like this patch is preventing my compiler >> (GCC 4.8) to perform some optimization. > >Does the "restrict" keyword make any difference? >e.g. in the function prototype, changing > struct netdev_flow_key *keys >to > struct netdev_flow_key *restrict keys > >Just a thought, not sure it'll help. I tried adding "restrict", but I didn't notice any differences. It seems that GCC decides to inline a different set of functions with this patch applied. Given the numbers, and given that we can restore the performance of the emc path in other ways, I'm in favour of this patch. Acked-by: Daniele Di Proietto <diproiet...@vmware.com> _______________________________________________ dev mailing list dev@openvswitch.org http://openvswitch.org/mailman/listinfo/dev
