On Thu, 2017-06-22 at 23:06 +1000, Michael Ellerman wrote:
> Paolo wrote:
> > when udp_recvmsg() is executed, on x86_64 and other archs, most skb
> > fields are on cold cachelines.
> > If the skb are linear and the kernel don't need to compute the udp
> > csum, only a handful of skb fields are required by udp_recvmsg().
> > Since we already use skb->dev_scratch to cache hot data, and
> > there are 32 bits unused on 64 bit archs, use such field to cache
> > as much data as we can, and try to prefetch on dequeue the relevant
> > fields that are left out.
> >
> > This can save up to 2 cache miss per packet.
> >
> > v1 -> v2:
> > - changed udp_dev_scratch fields types to u{32,16} variant,
> > replaced bitfiled with bool
> >
> > Signed-off-by: Paolo Abeni <pab...@redhat.com>
> > Acked-by: Eric Dumazet <eduma...@google.com>
> > ---
> > net/ipv4/udp.c | 114
> > +++++++++++++++++++++++++++++++++++++++++++++++++++------
> > 1 file changed, 103 insertions(+), 11 deletions(-)
>
> This appears to break wget on one of my machines.
>
> Networking in general is working, I'm able to SSH in, but then I can't
> do a wget.
Can you please check if the following patch fixes the issue? Only
compiled tested here.
Thanks!!!
---
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 067a607..80d89fe 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1446,16 +1446,19 @@ static struct sk_buff *__first_packet_length(struct
sock *sk,
{
struct sk_buff *skb;
- while ((skb = skb_peek(rcvq)) != NULL &&
- udp_lib_checksum_complete(skb)) {
- __UDP_INC_STATS(sock_net(sk), UDP_MIB_CSUMERRORS,
- IS_UDPLITE(sk));
- __UDP_INC_STATS(sock_net(sk), UDP_MIB_INERRORS,
- IS_UDPLITE(sk));
- atomic_inc(&sk->sk_drops);
- __skb_unlink(skb, rcvq);
- *total += skb->truesize;
- kfree_skb(skb);
+ while ((skb = skb_peek(rcvq)) != NULL) {
+ if (udp_lib_checksum_complete(skb)) {
+ __UDP_INC_STATS(sock_net(sk), UDP_MIB_CSUMERRORS,
+ IS_UDPLITE(sk));
+ __UDP_INC_STATS(sock_net(sk), UDP_MIB_INERRORS,
+ IS_UDPLITE(sk));
+ atomic_inc(&sk->sk_drops);
+ __skb_unlink(skb, rcvq);
+ *total += skb->truesize;
+ kfree_skb(skb);
+ } else {
+ udp_set_dev_scratch(skb);
+ }
}
return skb;
}
