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

[Bruce Richardson <bruce.richardson@intel.com>]

On Wed, Jun 05, 2019 at 02:32:27PM +0200, Maxime Coquelin wrote:
> 
> 
> 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.
> 
Patch looks ok to me, but I'm not the one to apply it.

/Bruce