From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by passt.top (Postfix) with ESMTP id 820C95A0082 for ; Wed, 14 Dec 2022 11:36:01 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1671014160; 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=X8g4ueJKLwhPwNve2CNhLAnBGYbpQU9oXbiKd0l2LYs=; b=fbwtihepqxH4Im+4AkZr7nUEojiUxw1+dxH3uZOvW+UmjH+JqAhbBDvkvtxFYIU6Y1F/me i8TAArH9c8vU/w93UBQAWJ3BML9qioelYkFYG1XeqpW0RhuFuP+hr0JGEpRtcGZJWBSDd1 i8ehUdeKLYmk8752itW35MWKjlkxQQc= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-495-TxA8XpzgN_WDvJKFVsXgNA-1; Wed, 14 Dec 2022 05:35:49 -0500 X-MC-Unique: TxA8XpzgN_WDvJKFVsXgNA-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 65620811E6E; Wed, 14 Dec 2022 10:35:49 +0000 (UTC) Received: from maya.cloud.tilaa.com (ovpn-208-4.brq.redhat.com [10.40.208.4]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 2B5ED492C14; Wed, 14 Dec 2022 10:35:49 +0000 (UTC) Date: Wed, 14 Dec 2022 11:35:46 +0100 From: Stefano Brivio To: David Gibson Subject: Re: [PATCH 4/8] udp: Receive multiple datagrams at once on the pasta sock->tap path Message-ID: <20221214113546.16942d3a@elisabeth> In-Reply-To: References: <20221205081425.2614425-1-david@gibson.dropbear.id.au> <20221205081425.2614425-5-david@gibson.dropbear.id.au> <20221213234847.6c723ad9@elisabeth> Organization: Red Hat MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.9 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Message-ID-Hash: BG4SORLPAYQSD7ZOXC5E7YVULXRJY5UA X-Message-ID-Hash: BG4SORLPAYQSD7ZOXC5E7YVULXRJY5UA 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: passt-dev@passt.top X-Mailman-Version: 3.3.3 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 Wed, 14 Dec 2022 12:42:14 +1100 David Gibson wrote: > On Tue, Dec 13, 2022 at 11:48:47PM +0100, Stefano Brivio wrote: > > Sorry for the long delay here, > > > > On Mon, 5 Dec 2022 19:14:21 +1100 > > David Gibson wrote: > > > > > Usually udp_sock_handler() will receive and forward multiple (up to 32) > > > datagrams in udp_sock_handler(), then forward them all to the tap > > > interface. For unclear reasons, though, when in pasta mode we will only > > > receive and forward a single datagram at a time. Change it to receive > > > multiple datagrams at once, like the other paths. > > > > This is explained in the commit message of 6c931118643c ("tcp, udp: > > Receive batching doesn't pay off when writing single frames to tap"). > > > > I think it's worth re-checking the throughput now as this path is a bit > > different, but unfortunately I didn't include this in the "perf" tests :( > > because at the time I introduced those I wasn't sure it even made sense to > > have traffic from the same host being directed to the tap device. > > > > The iperf3 runs were I observed this are actually the ones from the Podman > > demo. Ideally that case should be also checked in the perf/pasta_udp tests. > > Hm, ok. > > > How fundamental is this for the rest of the series? I couldn't find any > > actual dependency on this but I might be missing something. > > So the issue is that prior to this change in pasta we receive multiple > frames at once on the splice path, but one frame at a time on the tap > path. By the end of this series we can't do that any more, because we > don't know before the recvmmsg() which one we'll be doing. Oh, right, I see. Then let me add this path to the perf/pasta_udp test and check how relevant this is now, I'll get back to you in a bit. -- Stefano