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

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

On 6/5/19 2:52 PM, Bruce Richardson wrote:
> 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.

Ok, my bad. I'll switch to the right maintainer.

Thanks for the ack,
Maxime

> /Bruce
>