Messages in this thread | | | From | Jesper Dangaard Brouer <> | Subject | Re: [PATCH net-next 03/21] ethtool, stats: introduce standard XDP statistics | Date | Thu, 12 Aug 2021 14:19:30 +0200 |
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On 04/08/2021 18.44, Jakub Kicinski wrote: > On Wed, 4 Aug 2021 10:17:56 -0600 David Ahern wrote: >> On 8/4/21 6:36 AM, Jakub Kicinski wrote: > >> Does anyone have data that shows bumping a properly implemented counter >> causes a noticeable performance degradation and if so by how much? You >> mention 'yet another cacheline' but collecting stats on stack and >> incrementing the driver structs at the end of the napi loop should not >> have a huge impact versus the value the stats provide. > > Not sure, maybe Jesper has some numbers. Maybe Intel folks do?
(sorry, behind on emails after vacation ... just partly answering inside this thread, not checking if you did a smart counter impl.).
I don't have exact numbers, but I hope Magnus (Intel) would be motivated to validate performance degradation from this patchset. As I know Intel is hunting the DPDK numbers with AF_XDP-zc, where every last cycle *do* count.
My experience is that counters can easily hurt performance, without the developers noticing the small degradation's. As Ahern sketch out above (stats on stack + end of napi loop update), I do believe that a smart counter implementation is possible to hide this overhead (hopefully completely in the CPUs pipeline slots).
I do highly appreciate the effort to standardize the XDP stats! So, I do hope this can somehow move forward.
--Jesper
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