Re: [PATCH bpf-next v2 0/3] xdp: recycle Page Pool backed skbs built from XDP frames

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On 03/03/2023 14.32, Alexander Lobakin wrote:
Yeah, I still remember that "Who needs cpumap nowadays" (c), but anyway.

__xdp_build_skb_from_frame() missed the moment when the networking stack
became able to recycle skb pages backed by a page_pool. This was making
e.g. cpumap redirect even less effective than simple %XDP_PASS. veth was
also affected in some scenarios.
A lot of drivers use skb_mark_for_recycle() already, it's been almost
two years and seems like there are no issues in using it in the generic
code too. {__,}xdp_release_frame() can be then removed as it losts its
last user.
Page Pool becomes then zero-alloc (or almost) in the abovementioned
cases, too. Other memory type models (who needs them at this point)
have no changes.

Some numbers on 1 Xeon Platinum core bombed with 27 Mpps of 64-byte
IPv6 UDP, iavf w/XDP[0] (CONFIG_PAGE_POOL_STATS is enabled):

Plain %XDP_PASS on baseline, Page Pool driver:

src cpu Rx     drops  dst cpu Rx
   2.1 Mpps       N/A    2.1 Mpps

cpumap redirect (w/o leaving its node) on baseline:

What does it mean "without leaving its node" ?
I interpret this means BPF program CPU redirect to "same" CPU ?
Or does the "node" reference a NUMA node?


   6.8 Mpps  5.0 Mpps    1.8 Mpps

cpumap redirect with skb PP recycling:

Does this test use two CPUs?


   7.9 Mpps  5.7 Mpps    2.2 Mpps
                        +22% (from cpumap redir on baseline)
[0] https://github.com/alobakin/linux/commits/iavf-xdp

Alexander Lobakin (3):
   net: page_pool, skbuff: make skb_mark_for_recycle() always available
   xdp: recycle Page Pool backed skbs built from XDP frames
   xdp: remove unused {__,}xdp_release_frame()

  include/linux/skbuff.h |  4 ++--
  include/net/xdp.h      | 29 -----------------------------
  net/core/xdp.c         | 19 ++-----------------
  3 files changed, 4 insertions(+), 48 deletions(-)

---
 From v1[1]:
* make skb_mark_for_recycle() always available, otherwise there are build
   failures on non-PP systems (kbuild bot);
* 'Page Pool' -> 'page_pool' when it's about a page_pool instance, not
   API (Jesper);
* expanded test system info a bit in the cover letter (Jesper).

[1] https://lore.kernel.org/bpf/20230301160315.1022488-1-aleksander.lobakin@xxxxxxxxx




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