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Date: Fri, 14 Dec 2018 13:18:05 +0200
From: Ilias Apalodimas <ilias.apalodimas@...aro.org>
To: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc: "<netdev@...r.kernel.org>" <netdev@...r.kernel.org>,
Jaswinder Singh <jaswinder.singh@...aro.org>,
Masami Hiramatsu <masami.hiramatsu@...aro.org>,
Masahisa Kojima <masahisa.kojima@...aro.org>
Subject: Re: [net-next, PATCH 2/2] net: socionext: remove mmio reads on Tx
On Fri, Dec 14, 2018 at 11:59:00AM +0100, Ard Biesheuvel wrote:
> On Fri, 14 Dec 2018 at 09:59, Ilias Apalodimas
> <ilias.apalodimas@...aro.org> wrote:
> >
> > Currently the driver issues 2 mmio reads to figure out the number of
> > transmitted packets and clean them. We can get rid of the expensive
> > reads since BIT 31 of the Tx descriptor can be used for that.
> > We can also remove the budget counting of Tx completions since all of
> > the descriptors are not deliberately processed.
> >
>
> This last sentence reflects what we discussed off-line, right? That
> reaping used Tx descriptors shouldn't be counted against the budget,
> but should only occur if the budget is > 0 after processing the Rx
> queue?
yes
> > Performance numbers using pktgen are:
> > size pre-patch(pps) post-patch(pps)
> > 64 362483 427916
> > 128 358315 411686
> > 256 352725 389683
> > 512 215675 216464
> > 1024 113812 114442
> >
> > Signed-off-by: Ilias Apalodimas <ilias.apalodimas@...aro.org>
> > ---
> > drivers/net/ethernet/socionext/netsec.c | 97 ++++++++++++++-----------
> > 1 file changed, 54 insertions(+), 43 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/socionext/netsec.c b/drivers/net/ethernet/socionext/netsec.c
> > index 584a6b3f6542..05a0948ad929 100644
> > --- a/drivers/net/ethernet/socionext/netsec.c
> > +++ b/drivers/net/ethernet/socionext/netsec.c
> > @@ -257,7 +257,6 @@ struct netsec_desc_ring {
> > dma_addr_t desc_dma;
> > struct netsec_desc *desc;
> > void *vaddr;
> > - u16 pkt_cnt;
> > u16 head, tail;
> > };
> >
> > @@ -598,33 +597,26 @@ static void netsec_set_rx_de(struct netsec_priv *priv,
> > dring->desc[idx].len = desc->len;
> > }
> >
> > -static int netsec_clean_tx_dring(struct netsec_priv *priv, int budget)
> > +static bool netsec_clean_tx_dring(struct netsec_priv *priv)
> > {
> > struct netsec_desc_ring *dring = &priv->desc_ring[NETSEC_RING_TX];
> > unsigned int pkts, bytes;
> > -
> > - dring->pkt_cnt += netsec_read(priv, NETSEC_REG_NRM_TX_DONE_PKTCNT);
> > -
> > - if (dring->pkt_cnt < budget)
> > - budget = dring->pkt_cnt;
> > + struct netsec_de *entry;
> > + int tail = dring->tail;
> > + int cnt = 0;
> >
> > pkts = 0;
> > bytes = 0;
> > + entry = dring->vaddr + DESC_SZ * tail;
> >
> > - while (pkts < budget) {
> > + while (!(entry->attr & (1U << NETSEC_TX_SHIFT_OWN_FIELD)) &&
> > + cnt < DESC_NUM) {
> > struct netsec_desc *desc;
> > - struct netsec_de *entry;
> > - int tail, eop;
> > -
> > - tail = dring->tail;
> > -
> > - /* move tail ahead */
> > - dring->tail = (tail + 1) % DESC_NUM;
> > + int eop;
> >
> > desc = &dring->desc[tail];
> > - entry = dring->vaddr + DESC_SZ * tail;
> > -
> > eop = (entry->attr >> NETSEC_TX_LAST) & 1;
> > + dma_rmb();
> >
> > dma_unmap_single(priv->dev, desc->dma_addr, desc->len,
> > DMA_TO_DEVICE);
> > @@ -633,38 +625,51 @@ static int netsec_clean_tx_dring(struct netsec_priv *priv, int budget)
> > bytes += desc->skb->len;
> > dev_kfree_skb(desc->skb);
> > }
> > + /* clean up so netsec_uninit_pkt_dring() won't free the skb
> > + * again
> > + */
> > *desc = (struct netsec_desc){};
> > +
> > + /* entry->attr is not going to be accessed by the NIC until
> > + * netsec_set_tx_de() is called. No need for a dma_wmb() here
> > + */
> > + entry->attr = 1U << NETSEC_TX_SHIFT_OWN_FIELD;
> > + /* move tail ahead */
> > + dring->tail = (tail + 1) % DESC_NUM;
> > +
> > + tail = dring->tail;
> > + entry = dring->vaddr + DESC_SZ * tail;
> > + cnt++;
> > }
> > - dring->pkt_cnt -= budget;
> >
> > - priv->ndev->stats.tx_packets += budget;
> > + if (!cnt)
> > + return false;
> > +
> > + /* reading the register clears the irq */
> > + netsec_read(priv, NETSEC_REG_NRM_TX_DONE_PKTCNT);
> > +
> > + priv->ndev->stats.tx_packets += cnt;
> > priv->ndev->stats.tx_bytes += bytes;
> >
> > - netdev_completed_queue(priv->ndev, budget, bytes);
> > + netdev_completed_queue(priv->ndev, cnt, bytes);
> >
> > - return budget;
> > + return true;
> > }
> >
> > -static int netsec_process_tx(struct netsec_priv *priv, int budget)
> > +static void netsec_process_tx(struct netsec_priv *priv)
> > {
> > struct net_device *ndev = priv->ndev;
> > - int new, done = 0;
> > + bool cleaned;
> >
> > - do {
> > - new = netsec_clean_tx_dring(priv, budget);
> > - done += new;
> > - budget -= new;
> > - } while (new);
> > + cleaned = netsec_clean_tx_dring(priv);
> >
> > - if (done && netif_queue_stopped(ndev)) {
> > + if (cleaned && netif_queue_stopped(ndev)) {
> > /* Make sure we update the value, anyone stopping the queue
> > * after this will read the proper consumer idx
> > */
> > smp_wmb();
> > netif_wake_queue(ndev);
> > }
> > -
> > - return done;
> > }
> >
> > static void *netsec_alloc_rx_data(struct netsec_priv *priv,
> > @@ -813,24 +818,17 @@ static int netsec_process_rx(struct netsec_priv *priv, int budget)
> > static int netsec_napi_poll(struct napi_struct *napi, int budget)
> > {
> > struct netsec_priv *priv;
> > - int tx, rx, done, todo;
> > + int rx, done, todo;
> >
> > priv = container_of(napi, struct netsec_priv, napi);
> >
> > + netsec_process_tx(priv);
> > +
>
> So shouldn't we do this *after* processing Rx, and only if there is budget left?
I am not really sure, this would drown Tx processing if you had a bunch of
received packets that exhausted the budget.
Intel 1gbit drivers are doing something similar. They reclaim Tx prior to
processing Rx. The only thing that could be checked here i guess is keep the
napi poll running if *all* Tx descriptors were processed at some point instead
of re-enabling irqs.
>
> > todo = budget;
> > do {
> > - if (!todo)
> > - break;
> > -
> > - tx = netsec_process_tx(priv, todo);
> > - todo -= tx;
> > -
> > - if (!todo)
> > - break;
> > -
> > rx = netsec_process_rx(priv, todo);
> > todo -= rx;
> > - } while (rx || tx);
> > + } while (rx);
> >
> > done = budget - todo;
> >
> > @@ -1007,7 +1005,6 @@ static void netsec_uninit_pkt_dring(struct netsec_priv *priv, int id)
> >
> > dring->head = 0;
> > dring->tail = 0;
> > - dring->pkt_cnt = 0;
> >
> > if (id == NETSEC_RING_TX)
> > netdev_reset_queue(priv->ndev);
> > @@ -1030,6 +1027,7 @@ static void netsec_free_dring(struct netsec_priv *priv, int id)
> > static int netsec_alloc_dring(struct netsec_priv *priv, enum ring_id id)
> > {
> > struct netsec_desc_ring *dring = &priv->desc_ring[id];
> > + int i;
> >
> > dring->vaddr = dma_zalloc_coherent(priv->dev, DESC_SZ * DESC_NUM,
> > &dring->desc_dma, GFP_KERNEL);
> > @@ -1040,6 +1038,19 @@ static int netsec_alloc_dring(struct netsec_priv *priv, enum ring_id id)
> > if (!dring->desc)
> > goto err;
> >
> > + if (id == NETSEC_RING_TX) {
> > + for (i = 0; i < DESC_NUM; i++) {
> > + struct netsec_de *de;
> > +
> > + de = dring->vaddr + (DESC_SZ * i);
> > + /* de->attr is not going to be accessed by the NIC
> > + * until netsec_set_tx_de() is called.
> > + * No need for a dma_wmb() here
> > + */
> > + de->attr = 1U << NETSEC_TX_SHIFT_OWN_FIELD;
> > + }
> > + }
> > +
> > return 0;
> > err:
> > netsec_free_dring(priv, id);
> > --
> > 2.19.1
> >
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