Re: [dpdk-dev] [PATCH v2 00/16] vhost packed ring performance optimization

["Gavin Hu (Arm Technology China)" <Gavin.Hu@arm.com>]

Hi Marvin,

A general comment for the series, could you mark V1 Superseded?

/Gavin

> -----Original Message-----
> From: dev <dev-bounces@dpdk.org> On Behalf Of Marvin Liu
> Sent: Friday, September 20, 2019 12:36 AM
> To: maxime.coquelin@redhat.com; tiwei.bie@intel.com;
> zhihong.wang@intel.com
> Cc: dev@dpdk.org; Marvin Liu <yong.liu@intel.com>
> Subject: [dpdk-dev] [PATCH v2 00/16] vhost packed ring performance
> optimization
>
> Packed ring has more compact ring format and thus can significantly
> reduce the number of cache miss. It can lead to better performance.
> This has been approved in virtio user driver, on normal E5 Xeon cpu
> single core performance can raise 12%.
>
> http://mails.dpdk.org/archives/dev/2018-April/095470.html
>
> However vhost performance with packed ring performance was decreased.
> Through analysis, mostly extra cost was from the calculating of each
> descriptor flag which depended on ring wrap counter. Moreover, both
> frontend and backend need to write same descriptors which will cause
> cache contention. Especially when doing vhost enqueue function, virtio
> refill packed ring function may write same cache line when vhost doing
> enqueue function. This kind of extra cache cost will reduce the benefit
> of reducing cache misses.
>
> For optimizing vhost packed ring performance, vhost enqueue and dequeue
> function will be splitted into fast and normal path.
>
> Several methods will be taken in fast path:
>   Uroll burst loop function into more pieces.
>   Handle descriptors in one cache line simultaneously.
>   Prerequisite check that whether I/O space can copy directly into mbuf
>     space and vice versa.
>   Prerequisite check that whether descriptor mapping is successful.
>   Distinguish vhost used ring update function by enqueue and dequeue
>     function.
>   Buffer dequeue used descriptors as many as possible.
>   Update enqueue used descriptors by cache line.
>   Cache memory region structure for fast conversion.
>   Disable sofware prefetch is hardware can do better.
>
> After all these methods done, single core vhost PvP performance with 64B
> packet on Xeon 8180 can boost 40%.
>
> v2:
> - Utilize compiler's pragma to unroll loop, distinguish clang/icc/gcc
> - Buffered dequeue used desc number changed to (RING_SZ - PKT_BURST)
> - Optimize dequeue used ring update when in_order negotiated
>
> Marvin Liu (16):
>   vhost: add single packet enqueue function
>   vhost: unify unroll pragma parameter
>   vhost: add burst enqueue function for packed ring
>   vhost: add single packet dequeue function
>   vhost: add burst dequeue function
>   vhost: rename flush shadow used ring functions
>   vhost: flush vhost enqueue shadow ring by burst
>   vhost: add flush function for burst enqueue
>   vhost: buffer vhost dequeue shadow ring
>   vhost: split enqueue and dequeue flush functions
>   vhost: optimize enqueue function of packed ring
>   vhost: add burst and single zero dequeue functions
>   vhost: optimize dequeue function of packed ring
>   vhost: cache address translation result
>   vhost: check whether disable software pre-fetch
>   vhost: optimize packed ring dequeue when in-order
>
>  lib/librte_vhost/Makefile     |   24 +
>  lib/librte_vhost/rte_vhost.h  |   27 +
>  lib/librte_vhost/vhost.h      |   33 +
>  lib/librte_vhost/virtio_net.c | 1071 +++++++++++++++++++++++++++------
>  4 files changed, 960 insertions(+), 195 deletions(-)
>
> --
> 2.17.1

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