From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0173321C9EA for ; Fri, 14 Nov 2025 16:03:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763136187; cv=none; b=fIi398SEA3onvGUIEA2+vhqAJ3z42epmNt2Z+90Xai4S6ggF1lwjPkwP/l0qK8Ixo1+ebQXnzeF7ASS13utYlqsQ6+UAkXQJSdjcBW1bmPMGx9dbWGJx0v6Mtbu241pkM8TE+mLD/3paOHQ1AQdV1E5qRcuMlG4zjhmA/dBxaDM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763136187; c=relaxed/simple; bh=Gug63O31uXdMLrnpz+G89mRGIkLeG5Y311JrJGMg+YI=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=hkEgwE+nBAAuNOWGBMCoUcpfemYSpTH8eZanCfdxIFMPy0ZIp90tA0U7un6mtnv6HBM+PZl/Ydcd8KgZTM6Dz4Yh5SvKIK1woGbPg6ap8mCow/kJiOBffpx5U5Ob2b1pH9Zm4OKQXnkQNLJEwLcZE/nv9JR+nNOI/J7et2uUkJI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=tz9b3Qgb; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="tz9b3Qgb" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 29BEFC4CEF1; Fri, 14 Nov 2025 16:03:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1763136186; bh=Gug63O31uXdMLrnpz+G89mRGIkLeG5Y311JrJGMg+YI=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=tz9b3QgbWSfm2tO5hgG/g3P3mLgSWK1o/R441Kt1SOvEl79ZNtI5YP9oqfQaja8Cp +wc5sqZQX/+FX0XzRbBBEoQAVpYlgVPrHWDMtlgCaMSqYeT1df6i7PJjx4nWMH9Th4 shbJyr5FshB+YrVGthHM1FSpzb+YWdRhkPqXGJ93dg7WKYeDNITMeW9cuhPqAzXFLh QZ6Mx5zKo5njpQwJszD9U7RFEOSm5q28nVEj+/fK61pICdUtxBZzdzS0P5e3O0Iykl av4FvZZ13QpphAVYNHXOelUi0KjgOKMTV5CF3jI2pqQxSoR5D7SBzgHYVPxa2OuqNh s2u2yLCThKuJg== Date: Fri, 14 Nov 2025 08:03:05 -0800 From: Jakub Kicinski To: Eric Dumazet Cc: "David S . Miller" , Paolo Abeni , Simon Horman , Neal Cardwell , Kuniyuki Iwashima , netdev@vger.kernel.org, eric.dumazet@gmail.com Subject: Re: [PATCH net] tcp: reduce tcp_comp_sack_slack_ns default value to 10 usec Message-ID: <20251114080305.6c275a7d@kernel.org> In-Reply-To: References: <20251114135141.3810964-1-edumazet@google.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Fri, 14 Nov 2025 06:08:58 -0800 Eric Dumazet wrote: > On Fri, Nov 14, 2025 at 5:51=E2=80=AFAM Eric Dumazet wrote: > > > > net.ipv4.tcp_comp_sack_slack_ns current default value is too high. > > > > When a flow has many drops (1 % or more), and small RTT, adding 100 usec > > before sending SACK stalls the sender relying on getting SACK > > fast enough to keep the pipe busy. > > > > Decrease the default to 10 usec. > > > > This is orthogonal to Congestion Control heuristics to determine > > if drops are caused by congestion or not. > > > > Signed-off-by: Eric Dumazet =20 >=20 > This was meant for net-next, but applying this to net tree should be > fine as well. >=20 > No need for backports though. Sorry to piggy back on a random post but looks like the changes from a ~week ago made ncdevmem flaky:=20 https://netdev.bots.linux.dev/contest.html?executor=3Dvmksft-fbnic-qemu&tes= t=3Ddevmem-py Specifically it says: using ifindex=3D3 using queues 2..3 got tx dmabuf id=3D5 Connect to 2001:db8:1::2 37943 (via enp1s0) sendmsg_ret=3D6 ncdevmem: did not receive tx completion This is what was in the branch that made the test fail: [+] tcp: add net.ipv4.tcp_comp_sack_rtt_percent [+] net: increase skb_defer_max default to 128 [+] net: fix napi_consume_skb() with alien skbs [+] net: allow skb_release_head_state() to be called multiple times https://netdev.bots.linux.dev/static/nipa/branch_deltas/net-next-hw-2025-11= -08--00-00.html I'm guessing we need to take care of the uarg if we defer freeing=20 of Tx skbs..