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Date: Thu, 16 Jan 2014 13:53:40 +0200
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Michael Dalton <mwdalton@...gle.com>
Cc: "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
Eric Dumazet <edumazet@...gle.com>,
Rusty Russell <rusty@...tcorp.com.au>,
Jason Wang <jasowang@...hat.com>,
virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH net-next v3 5/5] virtio-net: initial rx sysfs support,
export mergeable rx buffer size
On Thu, Jan 16, 2014 at 01:38:46AM -0800, Michael Dalton wrote:
> Add initial support for per-rx queue sysfs attributes to virtio-net. If
> mergeable packet buffers are enabled, adds a read-only mergeable packet
> buffer size sysfs attribute for each RX queue.
>
> Signed-off-by: Michael Dalton <mwdalton@...gle.com>
> ---
> drivers/net/virtio_net.c | 66 +++++++++++++++++++++++++++++++++++++++++++++---
> 1 file changed, 62 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 3e82311..f315cbb 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -27,6 +27,7 @@
> #include <linux/slab.h>
> #include <linux/cpu.h>
> #include <linux/average.h>
> +#include <linux/seqlock.h>
>
> static int napi_weight = NAPI_POLL_WEIGHT;
> module_param(napi_weight, int, 0444);
> @@ -89,6 +90,12 @@ struct receive_queue {
> /* Average packet length for mergeable receive buffers. */
> struct ewma mrg_avg_pkt_len;
>
> + /* Sequence counter to allow sysfs readers to safely access stats.
> + * Assumes a single virtio-net writer, which is enforced by virtio-net
> + * and NAPI.
> + */
> + seqcount_t sysfs_seq;
> +
> /* Page frag for packet buffer allocation. */
> struct page_frag alloc_frag;
>
> @@ -416,7 +423,9 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> }
> }
>
> + write_seqcount_begin(&rq->sysfs_seq);
> ewma_add(&rq->mrg_avg_pkt_len, head_skb->len);
> + write_seqcount_end(&rq->sysfs_seq);
> return head_skb;
>
> err_skb:
Hmm this adds overhead just to prevent sysfs from getting wrong value.
Can't sysfs simply disable softirq while it's reading the value?
> @@ -604,18 +613,29 @@ static int add_recvbuf_big(struct receive_queue *rq, gfp_t gfp)
> return err;
> }
>
> -static int add_recvbuf_mergeable(struct receive_queue *rq, gfp_t gfp)
> +static unsigned int get_mergeable_buf_len(struct ewma *avg_pkt_len)
> {
> const size_t hdr_len = sizeof(struct virtio_net_hdr_mrg_rxbuf);
> + unsigned int len;
> +
> + len = hdr_len + clamp_t(unsigned int, ewma_read(avg_pkt_len),
> + GOOD_PACKET_LEN, PAGE_SIZE - hdr_len);
> + return ALIGN(len, MERGEABLE_BUFFER_ALIGN);
> +}
> +
> +static int add_recvbuf_mergeable(struct receive_queue *rq, gfp_t gfp)
> +{
> struct page_frag *alloc_frag = &rq->alloc_frag;
> char *buf;
> unsigned long ctx;
> int err;
> unsigned int len, hole;
>
> - len = hdr_len + clamp_t(unsigned int, ewma_read(&rq->mrg_avg_pkt_len),
> - GOOD_PACKET_LEN, PAGE_SIZE - hdr_len);
> - len = ALIGN(len, MERGEABLE_BUFFER_ALIGN);
> + /* avg_pkt_len is written only in NAPI rx softirq context. We may
> + * read avg_pkt_len without using the sysfs_seq seqcount, as this code
> + * is called only in NAPI rx softirq context or when NAPI is disabled.
> + */
> + len = get_mergeable_buf_len(&rq->mrg_avg_pkt_len);
> if (unlikely(!skb_page_frag_refill(len, alloc_frag, gfp)))
> return -ENOMEM;
>
> @@ -1557,6 +1577,7 @@ static int virtnet_alloc_queues(struct virtnet_info *vi)
> napi_weight);
>
> sg_init_table(vi->rq[i].sg, ARRAY_SIZE(vi->rq[i].sg));
> + seqcount_init(&vi->rq[i].sysfs_seq);
> ewma_init(&vi->rq[i].mrg_avg_pkt_len, 1, RECEIVE_AVG_WEIGHT);
> sg_init_table(vi->sq[i].sg, ARRAY_SIZE(vi->sq[i].sg));
> }
> @@ -1594,6 +1615,39 @@ err:
> return ret;
> }
>
> +#ifdef CONFIG_SYSFS
> +static ssize_t mergeable_rx_buffer_size_show(struct netdev_rx_queue *queue,
> + struct rx_queue_attribute *attribute, char *buf)
> +{
> + struct virtnet_info *vi = netdev_priv(queue->dev);
> + unsigned int queue_index = get_netdev_rx_queue_index(queue);
> + struct receive_queue *rq;
> + struct ewma avg;
> + unsigned int start;
> +
> + BUG_ON(queue_index >= vi->max_queue_pairs);
> + rq = &vi->rq[queue_index];
> + do {
> + start = read_seqcount_begin(&rq->sysfs_seq);
> + avg = rq->mrg_avg_pkt_len;
> + } while (read_seqcount_retry(&rq->sysfs_seq, start));
> + return sprintf(buf, "%u\n", get_mergeable_buf_len(&avg));
> +}
> +
> +static struct rx_queue_attribute mergeable_rx_buffer_size_attribute =
> + __ATTR_RO(mergeable_rx_buffer_size);
> +
> +static struct attribute *virtio_net_mrg_rx_attrs[] = {
> + &mergeable_rx_buffer_size_attribute.attr,
> + NULL
> +};
> +
> +static const struct attribute_group virtio_net_mrg_rx_group = {
> + .name = "virtio_net",
> + .attrs = virtio_net_mrg_rx_attrs
> +};
> +#endif
> +
> static int virtnet_probe(struct virtio_device *vdev)
> {
> int i, err;
> @@ -1708,6 +1762,10 @@ static int virtnet_probe(struct virtio_device *vdev)
> if (err)
> goto free_stats;
>
> +#ifdef CONFIG_SYSFS
> + if (vi->mergeable_rx_bufs)
> + dev->sysfs_rx_queue_group = &virtio_net_mrg_rx_group;
> +#endif
> netif_set_real_num_tx_queues(dev, vi->curr_queue_pairs);
> netif_set_real_num_rx_queues(dev, vi->curr_queue_pairs);
>
> --
> 1.8.5.2
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