Please try :
diff --git a/drivers/infiniband/ulp/ipoib/ipoib_ib.c
b/drivers/infiniband/ulp/ipoib/ipoib_ib.c
index 2cfa76f..9bdff21 100644
--- a/drivers/infiniband/ulp/ipoib/ipoib_ib.c
+++ b/drivers/infiniband/ulp/ipoib/ipoib_ib.c
@@ -112,6 +112,8 @@ static void ipoib_ud_skb_put_frags(struct
ipoib_dev_priv *priv,
if (ipoib_ud_need_sg(priv->max_ib_mtu)) {
skb_frag_t *frag = &skb_shinfo(skb)->frags[0];
unsigned int size;
+
+ prefetch(page_address(frag->page.p));
/*
* There is only two buffers needed for max_payload = 4K,
* first buf size is IPOIB_UD_HEAD_SIZE
On Wed, Apr 17, 2013 at 11:38 AM, Markus Stockhausen
<[email protected]> wrote:
>>
>>
>>
>>That's probably because of a cache line miss.
>>
>>The thing I don't really understand is that normally, the first cache
>>line (64 bytes) contains both the Ethernet header and IPv4 header.
>>
>>So what does this adapter in this respect ?
>>
>>I guess you should try to use IPOIB_UD_HEAD_SIZE=64 to use the whole
>>cache line.
>>
>>Many drivers use prefetch() to make sure cpu starts to bring this
>>cache line into cache as soon as possible.
>>
>>A single prefetch() call at the right place might help a lot.
>
> Hello,
>
> @Eric: Thanks for the tip.
>
> In the 4K MAX MTU IPoIB driver path ipoib_ib_handle_rx_wc() will
> produce an empty skb linear part with the whole data placed into
> the first fragment. napi_gro_receive() finally pulls the IP
> header out of the fragment into the linear part.
>
> As far as I understand the pull out of the fragment should come
> without additional cost when one calls a prefetch "long" before
> the skb_pull().
>
> I'm willing to check this out but I'm unsure if the IP header
> is aligned to a cache line of 64 bytes. As a simple guess I
> would implement the prefetch here:
>
> static void ipoib_ib_handle_rx_wc();
> ...
> skb_pull (skb, IB_GRH_BYTES);
>
> skb->protocol = ((struct ipoib_header *) skb->data)->proto;
> skb_reset_mac_header(skb);
> skb_pull(skb, IPOIB_ENCAP_LEN);
> +
> + if (ipoib_ud_need_sg(priv->max_ib_mtu))
> + prefetch(<whatever address>);
> ...
>
> Can you give me a hint what address one should put into the call?
>
> Thanks in advance.
>
> Markus
>
>
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