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

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

On 5/17/19 3:04 PM, David Marchand wrote:
> 
> 
> On Fri, May 17, 2019 at 2:23 PM Maxime Coquelin 
> <maxime.coquelin@redhat.com <mailto:maxime.coquelin@redhat.com>> 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.
> 
>     Maxime Coquelin (4):
>        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
> 
>     root (1):
>        eal/x86: force inlining of all memcpy and mov helpers
> 
> 
> root ? "oops" :-)

Indeed... Oops!

> 
> 
> -- 
> David Marchand