On 5/30/24 12:21 PM, Paul Barker wrote:
[...]
>>> This patch makes multiple changes that can't be separated:
>>>
>>> 1) Allocate plain RX buffers via a page pool instead of allocating
>>> SKBs, then use build_skb() when a packet is received.
>>> 2) For GbEth IP, reduce the RX buffer size to 2kB.
>>> 3) For GbEth IP, merge packets which span more than one RX descriptor
>>> as SKB fragments instead of copying data.
>>>
>>> Implementing (1) without (2) would require the use of an order-1 page
>>> pool (instead of an order-0 page pool split into page fragments) for
>>> GbEth.
>>>
>>> Implementing (2) without (3) would leave us no space to re-assemble
>>> packets which span more than one RX descriptor.
>>>
>>> Implementing (3) without (1) would not be possible as the network stack
>>> expects to use put_page() or page_pool_put_page() to free SKB fragments
>>> after an SKB is consumed.
>>>
>>> RX checksum offload support is adjusted to handle both linear and
>>> nonlinear (fragmented) packets.
>>>
>>> This patch gives the following improvements during testing with iperf3.
>>>
>>> * RZ/G2L:
>>> * TCP RX: same bandwidth at -43% CPU load (70% -> 40%)
>>> * UDP RX: same bandwidth at -17% CPU load (88% -> 74%)
>>>
>>> * RZ/G2UL:
>>> * TCP RX: +30% bandwidth (726Mbps -> 941Mbps)
>>> * UDP RX: +417% bandwidth (108Mbps -> 558Mbps)
>>>
>>> * RZ/G3S:
>>> * TCP RX: +64% bandwidth (562Mbps -> 920Mbps)
>>> * UDP RX: +420% bandwidth (90Mbps -> 468Mbps)
>>>
>>> * RZ/Five:
>>> * TCP RX: +217% bandwidth (145Mbps -> 459Mbps)
>>> * UDP RX: +470% bandwidth (20Mbps -> 114Mbps)
>>>
>>> There is no significant impact on bandwidth or CPU load in testing on
>>> RZ/G2H or R-Car M3N.
>>>
>>> Signed-off-by: Paul Barker <paul.barker.ct@xxxxxxxxxxxxxx>
[...]
>>> diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
>>> index dd92f074881a..bb7f7d44be6e 100644
>>> --- a/drivers/net/ethernet/renesas/ravb_main.c
>>> +++ b/drivers/net/ethernet/renesas/ravb_main.c
[...]
>>> + return 0;
>>> +}
>>> +
>>> static u32
>>> ravb_rx_ring_refill(struct net_device *ndev, int q, u32 count, gfp_t gfp_mask)
>>> {
>>> struct ravb_private *priv = netdev_priv(ndev);
>>> - const struct ravb_hw_info *info = priv->info;
>>> struct ravb_rx_desc *rx_desc;
>>> - dma_addr_t dma_addr;
>>> u32 i, entry;
>>>
>>> for (i = 0; i < count; i++) {
>>> entry = (priv->dirty_rx[q] + i) % priv->num_rx_ring[q];
>>> rx_desc = ravb_rx_get_desc(priv, q, entry);
>>> - rx_desc->ds_cc = cpu_to_le16(info->rx_max_desc_use);
>>>
>>> - if (!priv->rx_skb[q][entry]) {
>>> - priv->rx_skb[q][entry] = ravb_alloc_skb(ndev, info, gfp_mask);
>>> - if (!priv->rx_skb[q][entry])
>>> + if (!priv->rx_buffers[q][entry].page) {
>>> + if (unlikely(ravb_alloc_rx_buffer(ndev, q, entry,
>>
>> Well, IIRC Greg KH is against using unlikely() unless you have actually
>> instrumented the code and this gives an improvement... have you? :-)
>
> My understanding was that we should use unlikely() for error checking in
> hot code paths where we want the "good" path to be optimised. I can drop
> this if I'm wrong though.
OK, keep it... :-)
[...]
>>> @@ -865,7 +894,16 @@ static int ravb_rx_gbeth(struct net_device *ndev, int budget, int q)
>>> stats->rx_bytes += skb->len;
>>> napi_gro_receive(&priv->napi[q], skb);
>>> rx_packets++;
>>> +
>>> + /* Clear rx_1st_skb so that it will only be
>>> + * non-NULL when valid.
>>> + */
>>> + if (die_dt == DT_FEND)
>>> + priv->rx_1st_skb = NULL;
>>
>> Hm, can't we do this under *case* DT_FEND above?
>
> It makes more logical sense to me to do this as the last step, but I
> guess it's a little more optimal to do it earlier. I'll move it.
Looking at it once more, we can't... unless I'm missing s/th. :-)
> Thanks,
MBR, Sergey
