On Aug 13, Alexander Lobakin wrote: > From: Alexander Lobakin <aleksander.lobakin@xxxxxxxxx> > Date: Thu, 8 Aug 2024 13:57:00 +0200 > > > From: Lorenzo Bianconi <lorenzo.bianconi@xxxxxxxxxx> > > Date: Thu, 8 Aug 2024 06:54:06 +0200 > > > >>> Hi Alexander, > >>> > >>> On Tue, Jun 28, 2022, at 12:47 PM, Alexander Lobakin wrote: > >>>> cpumap has its own BH context based on kthread. It has a sane batch > >>>> size of 8 frames per one cycle. > >>>> GRO can be used on its own, adjust cpumap calls to the > >>>> upper stack to use GRO API instead of netif_receive_skb_list() which > >>>> processes skbs by batches, but doesn't involve GRO layer at all. > >>>> It is most beneficial when a NIC which frame come from is XDP > >>>> generic metadata-enabled, but in plenty of tests GRO performs better > >>>> than listed receiving even given that it has to calculate full frame > >>>> checksums on CPU. > >>>> As GRO passes the skbs to the upper stack in the batches of > >>>> @gro_normal_batch, i.e. 8 by default, and @skb->dev point to the > >>>> device where the frame comes from, it is enough to disable GRO > >>>> netdev feature on it to completely restore the original behaviour: > >>>> untouched frames will be being bulked and passed to the upper stack > >>>> by 8, as it was with netif_receive_skb_list(). > >>>> > >>>> Signed-off-by: Alexander Lobakin <alexandr.lobakin@xxxxxxxxx> > >>>> --- > >>>> kernel/bpf/cpumap.c | 43 ++++++++++++++++++++++++++++++++++++++----- > >>>> 1 file changed, 38 insertions(+), 5 deletions(-) > >>>> > >>> > >>> AFAICT the cpumap + GRO is a good standalone improvement. I think > >>> cpumap is still missing this. > > > > The only concern for having GRO in cpumap without metadata from the NIC > > descriptor was that when the checksum status is missing, GRO calculates > > the checksum on CPU, which is not really fast. > > But I remember sometimes GRO was faster despite that. > > > >>> > >>> I have a production use case for this now. We want to do some intelligent > >>> RX steering and I think GRO would help over list-ified receive in some cases. > >>> We would prefer steer in HW (and thus get existing GRO support) but not all > >>> our NICs support it. So we need a software fallback. > >>> > >>> Are you still interested in merging the cpumap + GRO patches? > > > > For sure I can revive this part. I was planning to get back to this > > branch and pick patches which were not related to XDP hints and send > > them separately. > > > >> > >> Hi Daniel and Alex, > >> > >> Recently I worked on a PoC to add GRO support to cpumap codebase: > >> - https://github.com/LorenzoBianconi/bpf-next/commit/a4b8264d5000ecf016da5a2dd9ac302deaf38b3e > >> Here I added GRO support to cpumap through gro-cells. > >> - https://github.com/LorenzoBianconi/bpf-next/commit/da6cb32a4674aa72401c7414c9a8a0775ef41a55 > >> Here I added GRO support to cpumap trough napi-threaded APIs (with a some > >> changes to them). > > > > Hmm, when I was testing it, adding a whole NAPI to cpumap was sorta > > overkill, that's why I separated GRO structure from &napi_struct. > > > > Let me maybe find some free time, I would then test all 3 solutions > > (mine, gro_cells, threaded NAPI) and pick/send the best? > > > >> > >> Please note I have not run any performance tests so far, just verified it does > >> not crash (I was planning to resume this work soon). Please let me know if it > >> works for you. > > I did tests on both threaded NAPI for cpumap and my old implementation > with a traffic generator and I have the following (in Kpps): > > direct Rx direct GRO cpumap cpumap GRO > baseline 2900 5800 2700 2700 (N/A) > threaded 2300 4000 > old GRO 2300 4000 out of my curiority, have you tested even the gro_cells one? Lorenzo > > IOW, > > 1. There are no differences in perf between Lorenzo's threaded NAPI > GRO implementation and my old implementation, but Lorenzo's is also > a very nice cleanup as it switches cpumap to threaded NAPI completely > and the final diffstat even removes more lines than adds, while mine > adds a bunch of lines and refactors a couple hundred, so I'd go with > his variant. > > 2. After switching to NAPI, the performance without GRO decreases (2.3 > Mpps vs 2.7 Mpps), but after enabling GRO the perf increases hugely > (4 Mpps vs 2.7 Mpps) even though the CPU needs to compute checksums > manually. > > Note that the code is not polished to the top and I also have a good > improvement for allocating skb heads from the percpu NAPI cache in my > old tree which I'm planning to add to the series, so the final > improvement will be even bigger. > > + after we find how to pass checksum hint to cpumap, it will be yet > another big improvement for GRO (current code won't benefit from > this at all) > > To Lorenzo: > > Would it be fine if I prepare a series containing your patch for > threaded NAPI for cpumap (I'd polish it and break into 2 or 3) + > skb allocation optimization and send it OR you wanted to send this > on your own? I'm fine with either, in the first case, everything > would land within one series with the respective credits; in case > of the latter, I'd need to send a followup :) > > >> > >> Regards, > >> Lorenzo > >> > >>> > >>> Thanks, > >>> Daniel > > Thanks, > Olek >
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