From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by passt.top (Postfix) with ESMTP id D4FA05A026D for ; Fri, 23 Jun 2023 13:02:12 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1687518131; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=mPmFKevCFZUfjX2qh2yzMbDDTJR4kz9vpXSKA+G9CRs=; b=cwUL5IbVwFod8Jo5RZez89xPNiNTEKFG8V5zcC2Ve73LCo0yr43BvxbDduYn7NYTaMDghq 6Fb9KS7SRqUrFlO3izPewxkAewAHF0Uskf8sAOQDyFSCT8FjNWIP2mctl9n84ELkDbxH/a Z6ecc4c0ddWKpDOkhYhv7fuvcUZS/oA= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-392-CGRh2l50NEqQhD2z0_77hA-1; Fri, 23 Jun 2023 07:02:10 -0400 X-MC-Unique: CGRh2l50NEqQhD2z0_77hA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 101003C108DA for ; Fri, 23 Jun 2023 11:02:10 +0000 (UTC) Received: from elisabeth (unknown [10.39.208.41]) by smtp.corp.redhat.com (Postfix) with ESMTPS id EDFC41121315; Fri, 23 Jun 2023 11:02:08 +0000 (UTC) Date: Fri, 23 Jun 2023 13:02:01 +0200 From: Stefano Brivio To: Jon Maloy Subject: Re: [RFC v2] tcp: add support for read with offset when using MSG_PEEK Message-ID: <20230623130106.68d0e058@elisabeth> In-Reply-To: <20230623021227.2625490-1-jmaloy@redhat.com> References: <20230623021227.2625490-1-jmaloy@redhat.com> Organization: Red Hat MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Message-ID-Hash: PV4DBAK4FVSIMYEUBARQLNUJV23F6J5I X-Message-ID-Hash: PV4DBAK4FVSIMYEUBARQLNUJV23F6J5I X-MailFrom: sbrivio@redhat.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: lvivier@redhat.com, dgibson@redhat.com, passt-dev@passt.top X-Mailman-Version: 3.3.8 Precedence: list List-Id: Development discussion and patches for passt Archived-At: Archived-At: List-Archive: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: On Thu, 22 Jun 2023 22:12:27 -0400 Jon Maloy wrote: > When reading received messages with MSG_PEEK, we sometines have to read > the leading bytes of the stream several times, only to reach the bytes > we really want. This is clearly non-optimal. > > What we would want is something similar to pread/preadv(), but working > even for tcp sockets. At the same time, we obviously don't want to add > any new arguments to the recv/recvmsg() calls. > > In this commit, we allow the user to set iovec.iov_base in the first > vector entry to NULL. This tells the socket to skip the first entry, > hence making the iov_len field of that entry indicate the offset value. > This way, there is no need to add any new arguments. Ah-ha! I'm glad you found an acceptable way to pass a NULL pointer there. :) > This change is simple and non-intrusive, and should be safe addition to > the socket API. We have measured it to give a throughput improvement of ...it would be nice to also do a bit of profiling with perf(1) -- that's where I originally noticed we were wasting cycles on filling up tcp_buf_discard. Plus, sure, there's also some value in dropping a useless 16 MiB buffer. If you need examples/inspiration: the pasta (automated) demo shows that, skip at 9:20 in: https://passt.top/passt/about/#pasta_2 (the one on the left) and that's simply done like this: https://passt.top/passt/tree/test/demo/pasta#n163 > 8-10 % for the protocol splicer 'passst', which is used in KubeVirt passt > containers. Those are virtual machines in containers -- but other than KubeVirt, passt is generally supported in libvirt (>= 9.2) with QEMU (>= 7.2) > Signed-off-by: Jon Maloy > > works with original msghdr > > Signed-off-by: Jon Maloy > --- > net/ipv4/tcp.c | 10 +++++++++- > 1 file changed, 9 insertions(+), 1 deletion(-) > > diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c > index 33f559f491c8..1d89337e89b6 100644 > --- a/net/ipv4/tcp.c > +++ b/net/ipv4/tcp.c > @@ -2428,6 +2428,7 @@ static int tcp_recvmsg_locked(struct sock *sk, struct msghdr *msg, size_t len, > struct tcp_sock *tp = tcp_sk(sk); > int copied = 0; > u32 peek_seq; > + u32 peek_offset; Kernel networking code observes the reverse-Christmas tree notation (at least for new additions), this would need to go after *tp: struct tcp_sock *tp = tcp_sk(sk); u32 peek_offset; > u32 *seq; > unsigned long used; > int err; > @@ -2435,7 +2436,6 @@ static int tcp_recvmsg_locked(struct sock *sk, struct msghdr *msg, size_t len, > long timeo; > struct sk_buff *skb, *last; > u32 urg_hole = 0; > - Probably not intended. > err = -ENOTCONN; > if (sk->sk_state == TCP_LISTEN) > goto out; > @@ -2469,6 +2469,14 @@ static int tcp_recvmsg_locked(struct sock *sk, struct msghdr *msg, size_t len, > if (flags & MSG_PEEK) { > peek_seq = tp->copied_seq; > seq = &peek_seq; > + if (msg->msg_iter.iov[0].iov_base == NULL) { > + peek_offset = msg->msg_iter.iov[0].iov_len; > + msg->msg_iter.iov = &msg->msg_iter.iov[1]; > + msg->msg_iter.nr_segs -= 1; Do you also need to make sure that nr_segs > 1 if iov[0].iov_base is NULL? I'm not sure if we need to check explicitly that msg_iter.iov[1] is valid here (but I haven't followed the whole path from the syscall handler). > + msg->msg_iter.count -= peek_offset; > + len -= peek_offset; > + *seq += peek_offset; > + } > } > > target = sock_rcvlowat(sk, flags & MSG_WAITALL, len); -- Stefano