| Message ID | 1533801739-15312-1-git-send-email-ilias.apalodimas@linaro.org |
|---|---|
| State | New |
| Headers | show |
| Series | [net-next,1/2] net: socionext: Use descriptor info instead of MMIO reads on Rx | expand |
On Thu, Aug 9, 2018 at 10:02 AM Ilias Apalodimas <ilias.apalodimas@linaro.org> wrote: > > MMIO reads for remaining packets in queue occur (at least)twice per > invocation of netsec_process_rx(). We can use the packet descriptor to > identify if it's owned by the hardware and break out, avoiding the more > expensive MMIO read operations. This has a ~2% increase on the pps of the > Rx path when tested with 64byte packets > > Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org> > --- > drivers/net/ethernet/socionext/netsec.c | 19 +++++-------------- > 1 file changed, 5 insertions(+), 14 deletions(-) > > diff --git a/drivers/net/ethernet/socionext/netsec.c b/drivers/net/ethernet/socionext/netsec.c > index 01589b6..ae32909 100644 > --- a/drivers/net/ethernet/socionext/netsec.c > +++ b/drivers/net/ethernet/socionext/netsec.c > @@ -657,8 +657,6 @@ static struct sk_buff *netsec_get_rx_pkt_data(struct netsec_priv *priv, > + if (de->attr & (1U << NETSEC_RX_PKT_OWN_FIELD)) > + break; > done++; Should this use READ_ONCE() to prevent the compiler from moving the access around? I see that netsec_get_rx_pkt_data() has a dma_rmb() before reading the data, which prevents the CPU from doing something wrong here, but not the compiler. Arnd
On Thu, Aug 09, 2018 at 05:37:15PM +0200, Arnd Bergmann wrote: > On Thu, Aug 9, 2018 at 10:02 AM Ilias Apalodimas > <ilias.apalodimas@linaro.org> wrote: > > > > MMIO reads for remaining packets in queue occur (at least)twice per > > invocation of netsec_process_rx(). We can use the packet descriptor to > > identify if it's owned by the hardware and break out, avoiding the more > > expensive MMIO read operations. This has a ~2% increase on the pps of the > > Rx path when tested with 64byte packets > > > > Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org> > > --- > > drivers/net/ethernet/socionext/netsec.c | 19 +++++-------------- > > 1 file changed, 5 insertions(+), 14 deletions(-) > > > > diff --git a/drivers/net/ethernet/socionext/netsec.c b/drivers/net/ethernet/socionext/netsec.c > > index 01589b6..ae32909 100644 > > --- a/drivers/net/ethernet/socionext/netsec.c > > +++ b/drivers/net/ethernet/socionext/netsec.c > > @@ -657,8 +657,6 @@ static struct sk_buff *netsec_get_rx_pkt_data(struct netsec_priv *priv, > > > + if (de->attr & (1U << NETSEC_RX_PKT_OWN_FIELD)) > > + break; > > done++; > > Should this use READ_ONCE() to prevent the compiler from moving the > access around? I see that netsec_get_rx_pkt_data() has a dma_rmb() > before reading the data, which prevents the CPU from doing something > wrong here, but not the compiler. > > Arnd As we discussed i'll send a V2 with the dma_rmb() right after the desc status read Thnaks Ilias
diff --git a/drivers/net/ethernet/socionext/netsec.c b/drivers/net/ethernet/socionext/netsec.c index 01589b6..ae32909 100644 --- a/drivers/net/ethernet/socionext/netsec.c +++ b/drivers/net/ethernet/socionext/netsec.c @@ -657,8 +657,6 @@ static struct sk_buff *netsec_get_rx_pkt_data(struct netsec_priv *priv, /* move tail ahead */ dring->tail = (dring->tail + 1) % DESC_NUM; - dring->pkt_cnt--; - return skb; } @@ -731,25 +729,18 @@ static int netsec_process_rx(struct netsec_priv *priv, int budget) struct netsec_desc_ring *dring = &priv->desc_ring[NETSEC_RING_RX]; struct net_device *ndev = priv->ndev; struct netsec_rx_pkt_info rx_info; - int done = 0, rx_num = 0; + int done = 0; struct netsec_desc desc; struct sk_buff *skb; u16 len; while (done < budget) { - if (!rx_num) { - rx_num = netsec_read(priv, NETSEC_REG_NRM_RX_PKTCNT); - dring->pkt_cnt += rx_num; - - /* move head 'rx_num' */ - dring->head = (dring->head + rx_num) % DESC_NUM; + u16 idx = dring->tail; + struct netsec_de *de = dring->vaddr + (DESC_SZ * idx); - rx_num = dring->pkt_cnt; - if (!rx_num) - break; - } + if (de->attr & (1U << NETSEC_RX_PKT_OWN_FIELD)) + break; done++; - rx_num--; skb = netsec_get_rx_pkt_data(priv, &rx_info, &desc, &len); if (unlikely(!skb) || rx_info.err_flag) { netif_err(priv, drv, priv->ndev,
MMIO reads for remaining packets in queue occur (at least)twice per invocation of netsec_process_rx(). We can use the packet descriptor to identify if it's owned by the hardware and break out, avoiding the more expensive MMIO read operations. This has a ~2% increase on the pps of the Rx path when tested with 64byte packets Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org> --- drivers/net/ethernet/socionext/netsec.c | 19 +++++-------------- 1 file changed, 5 insertions(+), 14 deletions(-) -- 2.7.4