Subject: Re: [PATCH net-next v6 0/5] remove page frag implementation in vhost_net

From: "Michael S. Tsirkin" <[email-masked]>
Date: Mon, 8 Apr 2024 03:48:26 -0400

On Wed, Feb 28, 2024 at 05:30:07PM +0800, Yunsheng Lin wrote:
> Currently there are three implementations for page frag:
> 
> 1. mm/page_alloc.c: net stack seems to be using it in the
>    rx part with 'struct page_frag_cache' and the main API
>    being page_frag_alloc_align().
> 2. net/core/sock.c: net stack seems to be using it in the
>    tx part with 'struct page_frag' and the main API being
>    skb_page_frag_refill().
> 3. drivers/vhost/net.c: vhost seems to be using it to build
>    xdp frame, and it's implementation seems to be a mix of
>    the above two.
> 
> This patchset tries to unfiy the page frag implementation a
> little bit by unifying gfp bit for order 3 page allocation
> and replacing page frag implementation in vhost.c with the
> one in page_alloc.c.
> 
> After this patchset, we are not only able to unify the page
> frag implementation a little, but also able to have about
> 0.5% performance boost testing by using the vhost_net_test
> introduced in the last patch.
> 
> Before this patchset:
> Performance counter stats for './vhost_net_test' (10 runs):
> 
>      305325.78 msec task-clock                       #    1.738 CPUs utilized               ( +-  0.12% )
>        1048668      context-switches                 #    3.435 K/sec                       ( +-  0.00% )
>             11      cpu-migrations                   #    0.036 /sec                        ( +- 17.64% )
>             33      page-faults                      #    0.108 /sec                        ( +-  0.49% )
>   244651819491      cycles                           #    0.801 GHz                         ( +-  0.43% )  (64)
>    64714638024      stalled-cycles-frontend          #   26.45% frontend cycles idle        ( +-  2.19% )  (67)
>    30774313491      stalled-cycles-backend           #   12.58% backend cycles idle         ( +-  7.68% )  (70)
>   201749748680      instructions                     #    0.82  insn per cycle
>                                               #    0.32  stalled cycles per insn     ( +-  0.41% )  (66.76%)
>    65494787909      branches                         #  214.508 M/sec                       ( +-  0.35% )  (64)
>     4284111313      branch-misses                    #    6.54% of all branches             ( +-  0.45% )  (66)
> 
>        175.699 +- 0.189 seconds time elapsed  ( +-  0.11% )
> 
> 
> After this patchset:
> Performance counter stats for './vhost_net_test' (10 runs):
> 
>      303974.38 msec task-clock                       #    1.739 CPUs utilized               ( +-  0.14% )
>        1048807      context-switches                 #    3.450 K/sec                       ( +-  0.00% )
>             14      cpu-migrations                   #    0.046 /sec                        ( +- 12.86% )
>             33      page-faults                      #    0.109 /sec                        ( +-  0.46% )
>   251289376347      cycles                           #    0.827 GHz                         ( +-  0.32% )  (60)
>    67885175415      stalled-cycles-frontend          #   27.01% frontend cycles idle        ( +-  0.48% )  (63)
>    27809282600      stalled-cycles-backend           #   11.07% backend cycles idle         ( +-  0.36% )  (71)
>   195543234672      instructions                     #    0.78  insn per cycle
>                                               #    0.35  stalled cycles per insn     ( +-  0.29% )  (69.04%)
>    62423183552      branches                         #  205.357 M/sec                       ( +-  0.48% )  (67)
>     4135666632      branch-misses                    #    6.63% of all branches             ( +-  0.63% )  (67)
> 
>        174.764 +- 0.214 seconds time elapsed  ( +-  0.12% )

The perf diff is in the noise, but the cleanup is nice.
Thanks!

Acked-by: Michael S. Tsirkin <[email-masked]>

> Changelog:
> V6: Add timeout for poll() and simplify some logic as suggested
>     by Jason.
> 
> V5: Address the comment from jason in vhost_net_test.c and the
>     comment about leaving out the gfp change for page frag in
>     sock.c as suggested by Paolo.
> 
> V4: Resend based on latest net-next branch.
> 
> V3:
> 1. Add __page_frag_alloc_align() which is passed with the align mask
>    the original function expected as suggested by Alexander.
> 2. Drop patch 3 in v2 suggested by Alexander.
> 3. Reorder patch 4 & 5 in v2 suggested by Alexander.
> 
> Note that placing this gfp flags handing for order 3 page in an inline
> function is not considered, as we may be able to unify the page_frag
> and page_frag_cache handling.
> 
> V2: Change 'xor'd' to 'masked off', add vhost tx testing for
>     vhost_net_test.
> 
> V1: Fix some typo, drop RFC tag and rebase on latest net-next.
> 
> Yunsheng Lin (5):
>   mm/page_alloc: modify page_frag_alloc_align() to accept align as an
>     argument
>   page_frag: unify gfp bits for order 3 page allocation
>   net: introduce page_frag_cache_drain()
>   vhost/net: remove vhost_net_page_frag_refill()
>   tools: virtio: introduce vhost_net_test
> 
>  drivers/net/ethernet/google/gve/gve_main.c |  11 +-
>  drivers/net/ethernet/mediatek/mtk_wed_wo.c |  17 +-
>  drivers/nvme/host/tcp.c                    |   7 +-
>  drivers/nvme/target/tcp.c                  |   4 +-
>  drivers/vhost/net.c                        |  91 ++--
>  include/linux/gfp.h                        |  16 +-
>  mm/page_alloc.c                            |  22 +-
>  net/core/skbuff.c                          |   9 +-
>  tools/virtio/.gitignore                    |   1 +
>  tools/virtio/Makefile                      |   8 +-
>  tools/virtio/linux/virtio_config.h         |   4 +
>  tools/virtio/vhost_net_test.c              | 532 +++++++++++++++++++++
>  12 files changed, 609 insertions(+), 113 deletions(-)
>  create mode 100644 tools/virtio/vhost_net_test.c
> 
> -- 
> 2.33.0
>