Re: [PATCH v2 net] splice: do not checksum AF_UNIX sockets

[Frederik Deweerdt]

On Tue, Dec 10, 2024 at 05:17:21PM +0900, Kuniyuki Iwashima wrote:
> From: Frederik Deweerdt <deweerdt.lkml@xxxxxxxxx>
> Date: Mon, 9 Dec 2024 21:06:48 -0800
> > When `skb_splice_from_iter` was introduced, it inadvertently added
> > checksumming for AF_UNIX sockets. This resulted in significant
> > slowdowns, for example when using sendfile over unix sockets.
> > 
> > Using the test code in [1] in my test setup (2G single core qemu),
> > the client receives a 1000M file in:
> > - without the patch: 1482ms (+/- 36ms)
> > - with the patch: 652.5ms (+/- 22.9ms)
> > 
> > This commit addresses the issue by marking checksumming as unnecessary in
> > `unix_stream_sendmsg`
> > 
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Frederik Deweerdt <deweerdt.lkml@xxxxxxxxx>
> > Fixes: 2e910b95329c ("net: Add a function to splice pages into an skbuff for MSG_SPLICE_PAGES")
> > ---
> 
> For the future submission, it would be nice to explain changes
> between versions and add the old patch link under '---' here.
> 
Will do, thank you.

> The patch itself looks good to me.
> 
> Reviewed-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
> 

Thanks!
Frederik
> >  net/unix/af_unix.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> > index 001ccc55ef0f..6b1762300443 100644
> > --- a/net/unix/af_unix.c
> > +++ b/net/unix/af_unix.c
> > @@ -2313,6 +2313,7 @@ static int unix_stream_sendmsg(struct socket *sock, struct msghdr *msg,
> >  		fds_sent = true;
> >  
> >  		if (unlikely(msg->msg_flags & MSG_SPLICE_PAGES)) {
> > +			skb->ip_summed = CHECKSUM_UNNECESSARY;
> >  			err = skb_splice_from_iter(skb, &msg->msg_iter, size,
> >  						   sk->sk_allocation);
> >  			if (err < 0) {
> > -- 
> > 2.44.1