Re: [PATCH net-next v3 6/8] virtio-net: xsk zero copy xmit kick by threshold

From: Jason Wang <jasowang@redhat.com>
To: Xuan Zhuo <xuanzhuo@linux.alibaba.com>, netdev@vger.kernel.org
Cc: "Michael S. Tsirkin" <mst@redhat.com>,
	"David S. Miller" <davem@davemloft.net>,
	"Jakub Kicinski" <kuba@kernel.org>,
	"Björn Töpel" <bjorn@kernel.org>,
	"Magnus Karlsson" <magnus.karlsson@intel.com>,
	"Jonathan Lemon" <jonathan.lemon@gmail.com>,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"Jesper Dangaard Brouer" <hawk@kernel.org>,
	"John Fastabend" <john.fastabend@gmail.com>,
	"Andrii Nakryiko" <andrii@kernel.org>,
	"Martin KaFai Lau" <kafai@fb.com>,
	"Song Liu" <songliubraving@fb.com>, "Yonghong Song" <yhs@fb.com>,
	"KP Singh" <kpsingh@kernel.org>,
	virtualization@lists.linux-foundation.org, bpf@vger.kernel.org,
	"Dust Li" <dust.li@linux.alibaba.com>
Subject: Re: [PATCH net-next v3 6/8] virtio-net: xsk zero copy xmit kick by threshold
Date: Tue, 6 Apr 2021 14:59:00 +0800	[thread overview]
Message-ID: <b04d7110-95ec-0aec-a802-631baf260a62@redhat.com> (raw)
In-Reply-To: <20210331071139.15473-7-xuanzhuo@linux.alibaba.com>

在 2021/3/31 下午3:11, Xuan Zhuo 写道:
> After testing, the performance of calling kick every time is not stable.
> And if all the packets are sent and kicked again, the performance is not
> good. So add a module parameter to specify how many packets are sent to
> call a kick.
>
> 8 is a relatively stable value with the best performance.

Please add some perf numbers here.

Thanks

>
> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> Reviewed-by: Dust Li <dust.li@linux.alibaba.com>
> ---
>   drivers/net/virtio_net.c | 23 ++++++++++++++++++++---
>   1 file changed, 20 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 259fafcf6028..d7e95f55478d 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -29,10 +29,12 @@ module_param(napi_weight, int, 0444);
>   
>   static bool csum = true, gso = true, napi_tx = true;
>   static int xsk_budget = 32;
> +static int xsk_kick_thr = 8;
>   module_param(csum, bool, 0444);
>   module_param(gso, bool, 0444);
>   module_param(napi_tx, bool, 0644);
>   module_param(xsk_budget, int, 0644);
> +module_param(xsk_kick_thr, int, 0644);
>   
>   /* FIXME: MTU in config. */
>   #define GOOD_PACKET_LEN (ETH_HLEN + VLAN_HLEN + ETH_DATA_LEN)
> @@ -2612,6 +2614,8 @@ static int virtnet_xsk_xmit_batch(struct send_queue *sq,
>   	struct xdp_desc desc;
>   	int err, packet = 0;
>   	int ret = -EAGAIN;
> +	int need_kick = 0;
> +	int kicks = 0;
>   
>   	if (sq->xsk.last_desc.addr) {
>   		err = virtnet_xsk_xmit(sq, pool, &sq->xsk.last_desc);
> @@ -2619,6 +2623,7 @@ static int virtnet_xsk_xmit_batch(struct send_queue *sq,
>   			return -EBUSY;
>   
>   		++packet;
> +		++need_kick;
>   		--budget;
>   		sq->xsk.last_desc.addr = 0;
>   	}
> @@ -2642,13 +2647,25 @@ static int virtnet_xsk_xmit_batch(struct send_queue *sq,
>   		}
>   
>   		++packet;
> +		++need_kick;
> +		if (need_kick > xsk_kick_thr) {
> +			if (virtqueue_kick_prepare(sq->vq) &&
> +			    virtqueue_notify(sq->vq))
> +				++kicks;
> +
> +			need_kick = 0;
> +		}
>   	}
>   
>   	if (packet) {
> -		if (virtqueue_kick_prepare(sq->vq) &&
> -		    virtqueue_notify(sq->vq)) {
> +		if (need_kick) {
> +			if (virtqueue_kick_prepare(sq->vq) &&
> +			    virtqueue_notify(sq->vq))
> +				++kicks;
> +		}
> +		if (kicks) {
>   			u64_stats_update_begin(&sq->stats.syncp);
> -			sq->stats.kicks += 1;
> +			sq->stats.kicks += kicks;
>   			u64_stats_update_end(&sq->stats.syncp);
>   		}
>   