Re: [dpdk-dev] [PATCH v3 0/5] vhost: I-cache pressure optimizations

[Maxime Coquelin <maxime.coquelin@redhat.com>]

On 5/29/19 3:04 PM, Maxime Coquelin wrote:
> Some OVS-DPDK PVP benchmarks show a performance drop
> when switching from DPDK v17.11 to v18.11.
> 
> With the addition of packed ring layout support,
> rte_vhost_enqueue_burst and rte_vhost_dequeue_burst
> became very large, and only a part of the instructions
> are executed (either packed or split ring used).
> 
> This series aims at improving the I-cache pressure,
> first by un-inlining split and packed rings, but
> also by moving parts considered as cold in dedicated
> functions (dirty page logging, fragmented descriptors
> buffer management added for CVE-2018-1059).
> 
> With the series applied, size of the enqueue and
> dequeue split paths is reduced significantly:
> 
> +---------+--------------------+---------------------+
> | Version | Enqueue split path |  Dequeue split path |
> +---------+--------------------+---------------------+
> | v19.05  | 16461B             | 25521B              |
> | +series | 7286B              | 11285B              |
> +---------+--------------------+---------------------+
> 
> Using perf tool to monitor iTLB-load-misses event
> while doing PVP benchmark with testpmd as vswitch,
> we can see the number of iTLB misses being reduced:
> 
> - v19.05:
> # perf stat --repeat 10  -C 2,3  -e iTLB-load-miss -- sleep 10
> 
>   Performance counter stats for 'CPU(s) 2,3' (10 runs):
> 
>               2,438      iTLB-load-miss                                                ( +- 13.43% )
> 
>         10.00058928 +- 0.00000336 seconds time elapsed  ( +-  0.00% )
> 
> - +series:
> # perf stat --repeat 10  -C 2,3  -e iTLB-load-miss -- sleep 10
> 
>   Performance counter stats for 'CPU(s) 2,3' (10 runs):
> 
>                  55      iTLB-load-miss                                                ( +- 10.08% )
> 
>         10.00059466 +- 0.00000283 seconds time elapsed  ( +-  0.00% )
> 
> The series also force the inlining of some rte_memcpy
> helpers, as by adding packed ring support, some of them
> were not more inlined but embedded as functions in
> the virtio_net object file, which was not expected.
> 
> Finally, the series simplifies the descriptors buffers
> prefetching, by doing it in the recently introduced
> descriptor buffer mapping function.
> 
> v3:
> ===
>   - Prefix alloc_copy_ind_table with vhost_ (Mattias)
>   - Remove double new line (Tiwei)
>   - Fix grammar error in patch 3's commit message (Jens)
>   - Force noinline for hear copy functions (Mattias)
>   - Fix dst assignement in copy_hdr_from_desc (Tiwei)
> 
> v2:
> ===
>   - Fix checkpatch issue
>   - Reset author for patch 5 (David)
>   - Force non-inlining in patch 2 (David)
>   - Fix typo in path 3 commit message (David)
> 
> Maxime Coquelin (5):
>    vhost: un-inline dirty pages logging functions
>    vhost: do not inline packed and split functions
>    vhost: do not inline unlikely fragmented buffers code
>    vhost: simplify descriptor's buffer prefetching
>    eal/x86: force inlining of all memcpy and mov helpers
> 
>   .../common/include/arch/x86/rte_memcpy.h      |  18 +-
>   lib/librte_vhost/vdpa.c                       |   2 +-
>   lib/librte_vhost/vhost.c                      | 164 +++++++++++++++++
>   lib/librte_vhost/vhost.h                      | 165 ++----------------
>   lib/librte_vhost/virtio_net.c                 | 140 +++++++--------
>   5 files changed, 251 insertions(+), 238 deletions(-)
> 


Applied patches 1 to 4 to dpdk-next-virtio/master.

Bruce, I'm assigning patch 5 to you in Patchwork, as this is not
vhost/virtio specific.

Thanks,
Maxime