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[76.103.20.67]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2152751571bsm35731825ad.222.2024.11.29.20.05.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 29 Nov 2024 20:05:23 -0800 (PST) Date: Fri, 29 Nov 2024 20:05:20 -0800 From: Frederik Deweerdt To: Cong Wang Cc: netdev@vger.kernel.org, dhowells@redhat.com Subject: Re: [PATCH net] splice: do not checksum AF_UNIX sockets Message-ID: References: Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Fri, Nov 29, 2024 at 05:43:04PM -0800, Cong Wang wrote: > On Fri, Nov 29, 2024 at 03:20:14PM -0800, Frederik Deweerdt wrote: > > When `skb_splice_from_iter` was introduced, it inadvertently added > > checksumming for AF_UNIX sockets. This resulted in significant > > slowdowns, as when using sendfile over unix sockets. > > > > Using the test code [1] in my test setup (2G, single core x86_64 qemu), > > the client receives a 1000M file in: > > - without the patch: 1577ms (+/- 36.1ms) > > - with the patch: 725ms (+/- 28.3ms) > > > > This commit skips addresses the issue by skipping checksumming when > > splice occurs a AF_UNIX socket. > > > > [1] https://gist.github.com/deweerdt/a3ee2477d1d87524cf08618d3c179f06 > > > > Signed-off-by: Frederik Deweerdt > > Fixes: 2e910b95329c ("net: Add a function to splice pages into an skbuff for MSG_SPLICE_PAGES") > > --- > > net/core/skbuff.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/net/core/skbuff.c b/net/core/skbuff.c > > index 6841e61a6bd0..49e4f9ab625f 100644 > > --- a/net/core/skbuff.c > > +++ b/net/core/skbuff.c > > @@ -7233,7 +7233,7 @@ ssize_t skb_splice_from_iter(struct sk_buff *skb, struct iov_iter *iter, > > goto out; > > } > > > > - if (skb->ip_summed == CHECKSUM_NONE) > > + if (skb->ip_summed == CHECKSUM_NONE && skb->sk->sk_family != AF_UNIX) > > Are you sure it is always safe to dereferene skb->sk here? I am not sure > about the KCM socket case. > > Instead of checking skb->sk->sk_family, why not just pass an additional > boolean parameter to this function? > I saw that every caller was dereferrencing an `sk`, but you are right that that a boolean would be safer. I'll resend an updated version. Thanks, Frederik