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Date: Fri, 3 Feb 2023 18:26:11 -0800
From: William Tu <u9012063@...il.com>
To: Alexander Lobakin <alexandr.lobakin@...el.com>
Cc: netdev@...r.kernel.org, jsankararama@...are.com, gyang@...are.com,
doshir@...are.com, alexander.duyck@...il.com, bang@...are.com,
Yifeng Sun <yifengs@...are.com>,
Alexander Duyck <alexanderduyck@...com>
Subject: Re: [RFC PATCH net-next v15] vmxnet3: Add XDP support.
Hi Alexander,
Thanks again for your review!
On Mon, Jan 30, 2023 at 4:26 AM Alexander Lobakin
<alexandr.lobakin@...el.com> wrote:
>
> From: William Tu <u9012063@...il.com>
> Date: Fri, 27 Jan 2023 08:30:27 -0800
>
> > The patch adds native-mode XDP support: XDP DROP, PASS, TX, and REDIRECT.
> >
> > Background:
> > The vmxnet3 rx consists of three rings: ring0, ring1, and dataring.
> > For r0 and r1, buffers at r0 are allocated using alloc_skb APIs and dma
> > mapped to the ring's descriptor. If LRO is enabled and packet size larger
> > than 3K, VMXNET3_MAX_SKB_BUF_SIZE, then r1 is used to mapped the rest of
> > the buffer larger than VMXNET3_MAX_SKB_BUF_SIZE. Each buffer in r1 is
> > allocated using alloc_page. So for LRO packets, the payload will be in one
> > buffer from r0 and multiple from r1, for non-LRO packets, only one
> > descriptor in r0 is used for packet size less than 3k.
>
> [...]
>
> > @@ -1404,6 +1496,8 @@ vmxnet3_rq_rx_complete(struct vmxnet3_rx_queue *rq,
> > struct Vmxnet3_RxDesc rxCmdDesc;
> > struct Vmxnet3_RxCompDesc rxComp;
> > #endif
> > + bool need_flush = false;
> > +
> > vmxnet3_getRxComp(rcd, &rq->comp_ring.base[rq->comp_ring.next2proc].rcd,
> > &rxComp);
> > while (rcd->gen == rq->comp_ring.gen) {
> > @@ -1444,6 +1538,31 @@ vmxnet3_rq_rx_complete(struct vmxnet3_rx_queue *rq,
> > goto rcd_done;
> > }
> >
> > + if (rcd->sop && rcd->eop && vmxnet3_xdp_enabled(adapter)) {
>
> Hmm, it's a relatively big block of code for one `if`. I mean, could we
> do it like that?
>
> if (!rcd->sop || !vmxnet3_xdp_enabled(adapter))
> goto skip_xdp;
>
> if (VMXNET3_RX_DATA_RING(adapter, rcd->rqID)) {
> ...
>
> This way you would save 1 indent level and make code a little bit more
> readable.
> But it might be a matter of personal tastes :) Just noticed you have
> this `skip_xdp` label anyway, why not reuse it here.
Good idea, this function has high indent level and this is a good idea.
I will do it.
>
> > + struct sk_buff *skb_xdp_pass;
> > + int act;
> > +
> > + if (VMXNET3_RX_DATA_RING(adapter, rcd->rqID)) {
> > + ctx->skb = NULL;
> > + goto skip_xdp; /* Handle it later. */
> > + }
> > +
> > + if (rbi->buf_type != VMXNET3_RX_BUF_XDP)
> > + goto rcd_done;
> > +
> > + act = vmxnet3_process_xdp(adapter, rq, rcd, rbi, rxd,
> > + &skb_xdp_pass);
> > + if (act == XDP_PASS) {
> > + ctx->skb = skb_xdp_pass;
> > + goto sop_done;
> > + }
> > + ctx->skb = NULL;
> > + if (act == XDP_REDIRECT)
> > + need_flush = true;
>
> need_flush |= act == XDP_REDIRECT;
>
> But this looks a big ugly to be honest, I just wrote it to show off a
> bit :D Your `if` is perfectly fine, not even sure the line I wrote above
> produces more optimized object code.
ha, ok. Good to know there is another option.
>
> > + goto rcd_done;
> > + }
> > +skip_xdp:
> > +
> > if (rcd->sop) { /* first buf of the pkt */
> > bool rxDataRingUsed;
> > u16 len;
> > @@ -1452,7 +1571,8 @@ vmxnet3_rq_rx_complete(struct vmxnet3_rx_queue *rq,
> > (rcd->rqID != rq->qid &&
> > rcd->rqID != rq->dataRingQid));
> >
> > - BUG_ON(rbi->buf_type != VMXNET3_RX_BUF_SKB);
> > + BUG_ON(rbi->buf_type != VMXNET3_RX_BUF_SKB &&
> > + rbi->buf_type != VMXNET3_RX_BUF_XDP);
> > BUG_ON(ctx->skb != NULL || rbi->skb == NULL);
> >
> > if (unlikely(rcd->len == 0)) {
> > @@ -1470,6 +1590,26 @@ vmxnet3_rq_rx_complete(struct vmxnet3_rx_queue *rq,
> > rxDataRingUsed =
> > VMXNET3_RX_DATA_RING(adapter, rcd->rqID);
> > len = rxDataRingUsed ? rcd->len : rbi->len;
> > +
> > + if (rxDataRingUsed && vmxnet3_xdp_enabled(adapter)) {
>
> Maybe save 1 level here as well:
cool, will do it.
>
> if (!rxDataRingUsed || !vmxnet3_xdp_enabled(ad))
> goto alloc_skb;
>
> sz = rcd->rxdIdx * ...
>
> > + struct sk_buff *skb_xdp_pass;
> > + size_t sz;
> > + int act;
> > +
> > + sz = rcd->rxdIdx * rq->data_ring.desc_size;
> > + act = vmxnet3_process_xdp_small(adapter, rq,
> > + &rq->data_ring.base[sz],
> > + rcd->len,
> > + &skb_xdp_pass);
> > + if (act == XDP_PASS) {
> > + ctx->skb = skb_xdp_pass;
> > + goto sop_done;
> > + }
> > + if (act == XDP_REDIRECT)
> > + need_flush = true;
> > +
> > + goto rcd_done;
> > + }
>
> alloc_skb:
>
> > new_skb = netdev_alloc_skb_ip_align(adapter->netdev,
> > len);
> > if (new_skb == NULL) {
>
> [...]
>
> > @@ -217,6 +221,9 @@ struct vmxnet3_tq_driver_stats {
> > u64 linearized; /* # of pkts linearized */
> > u64 copy_skb_header; /* # of times we have to copy skb header */
> > u64 oversized_hdr;
> > +
> > + u64 xdp_xmit;
> > + u64 xdp_xmit_err;
>
> Sorry for missing this earlier... You use u64 here for stats and
> previously we were using it for the stats, but then u64_stat_t was
> introduced to exclude partial updates and tearing. I know there are
> stats already in u64 above, but maybe right now is the best time to use
> u64_stat_t for the new fields? :)
thanks for the suggestion, I read through the u64_stats_t.
if I replace with u64_stats_t, then there are several places
to replace using u64_stats_init, update, ....
I will keep this as future work or separate patch.
>
> > };
> >
> > struct vmxnet3_tx_ctx {
> > @@ -253,12 +260,13 @@ struct vmxnet3_tx_queue {
> > * stopped */
> > int qid;
> > u16 txdata_desc_size;
> > -} __attribute__((__aligned__(SMP_CACHE_BYTES)));
> > +} ____cacheline_aligned;
> >
> > enum vmxnet3_rx_buf_type {
> > VMXNET3_RX_BUF_NONE = 0,
> > VMXNET3_RX_BUF_SKB = 1,
> > - VMXNET3_RX_BUF_PAGE = 2
> > + VMXNET3_RX_BUF_PAGE = 2,
> > + VMXNET3_RX_BUF_XDP = 3,
> > };
> >
> > #define VMXNET3_RXD_COMP_PENDING 0
> > @@ -285,6 +293,12 @@ struct vmxnet3_rq_driver_stats {
> > u64 drop_err;
> > u64 drop_fcs;
> > u64 rx_buf_alloc_failure;
> > +
> > + u64 xdp_packets; /* Total packets processed by XDP. */
> > + u64 xdp_tx;
> > + u64 xdp_redirects;
> > + u64 xdp_drops;
> > + u64 xdp_aborted;
>
> (same)
thanks! Will be future work or separate patch.
>
> > };
> >
> > struct vmxnet3_rx_data_ring {
>
> [...]
>
> > +static int
> > +vmxnet3_xdp_xmit_frame(struct vmxnet3_adapter *adapter,
> > + struct xdp_frame *xdpf,
> > + struct vmxnet3_tx_queue *tq, bool dma_map)
> > +{
> > + struct vmxnet3_tx_buf_info *tbi = NULL;
> > + union Vmxnet3_GenericDesc *gdesc;
> > + struct vmxnet3_tx_ctx ctx;
> > + int tx_num_deferred;
> > + struct page *page;
> > + u32 buf_size;
> > + int ret = 0;
> > + u32 dw2;
> > +
> > + dw2 = (tq->tx_ring.gen ^ 0x1) << VMXNET3_TXD_GEN_SHIFT;
> > + dw2 |= xdpf->len;
> > + ctx.sop_txd = tq->tx_ring.base + tq->tx_ring.next2fill;
> > + gdesc = ctx.sop_txd;
> > +
> > + buf_size = xdpf->len;
> > + tbi = tq->buf_info + tq->tx_ring.next2fill;
> > +
> > + if (vmxnet3_cmd_ring_desc_avail(&tq->tx_ring) == 0) {
> > + tq->stats.tx_ring_full++;
> > + return -ENOSPC;
> > + }
> > +
> > + tbi->map_type = VMXNET3_MAP_XDP;
> > + if (dma_map) { /* ndo_xdp_xmit */
> > + tbi->dma_addr = dma_map_single(&adapter->pdev->dev,
> > + xdpf->data, buf_size,
> > + DMA_TO_DEVICE);
> > + if (dma_mapping_error(&adapter->pdev->dev, tbi->dma_addr))
> > + return -EFAULT;
> > + tbi->map_type |= VMXNET3_MAP_SINGLE;
> > + } else { /* XDP buffer from page pool */
> > + page = virt_to_head_page(xdpf->data);
>
> Nit: your page pools are always order-0, thus you could shortcut those
> virt_to_head_page() throughout the drivers to just virt_to_page() and
> save at least 1 unlikely() condition check this way (it will always be
> false for the pages coming from your page pools). I remember we had huge
> CPU load point on this compound_head() check inside virt_to_head_page()...
good point! this avoids the _compound_head call
Will do it in next version
>
> > + tbi->dma_addr = page_pool_get_dma_addr(page) +
> > + XDP_PACKET_HEADROOM;
> > + dma_sync_single_for_device(&adapter->pdev->dev,
> > + tbi->dma_addr, buf_size,
> > + DMA_BIDIRECTIONAL);
> > + }
>
> [...]
>
> Those are some minors/propositions, up to you whether to address the
> rest was addressed perfectly by you, thanks!
>
> Reviewed-by: Alexander Lobakin <alexandr.lobakin@...el.com>
Thanks again for your time to review the patch. Working on next version now.
William
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