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 BAED122D4D3 for ; Mon, 16 Feb 2026 18:11:10 +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=1771265470; cv=none; b=XBWaPUCONI6JkotsyM45sXuBfamffg0/ay63hsw6LAiV8LenmSvf7d5cUiOG/jia9m49I0TWc1eS2um/zaJ8AqfYxHbluEb7YlxsvLC9CCf3LIW4Mq+4apWwdcxBSvFk4A5ppD3ZTG/I+2CYksZBHlXavTQevx+tgUYGK2kOYAY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771265470; c=relaxed/simple; bh=YvpKE+f9MXWcsTM3Nco/1s7RFnOf+UexpP3V25U1vpw=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=MtEscrFtGi3p9Zs+H+HbbolWHkvttJenb48zrpOtwtWBi0Zg427sCjTr2Od7VCTMou33S4MsaYDrTvsuQm739qst2jCzsnW89h03EnxgVudsiNHiv24jeItAMCAQpzqbobbcL4cJit0WAGwmqOYDlNK9rrnTCD/MOKCWp1KV2Pc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ZlMi4+W0; 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="ZlMi4+W0" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D6F46C116C6; Mon, 16 Feb 2026 18:11:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1771265470; bh=YvpKE+f9MXWcsTM3Nco/1s7RFnOf+UexpP3V25U1vpw=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=ZlMi4+W0JZUhthXpIVjYFHVEwZrmlqq9AfbPsMrXYP7d9ZYIOUAEo/xd1k19l93eZ yPKhW0WFyiT5gOHdiqxy60cr4tXcBmeoClcm+4SpTXcZR+ll+4e5d99Q63+cLTZuqu PvKa/yNwhLR//LWV0JnzO609JonJUIs8hdJyJayD7wiWk1YfvQjd5f5KuwelgNQuVJ Vt6RK12ogc8SmW1kzuloMC8Xto/8qEByQc2HXi4mv6ZEG53FJ30uuPUDFwpNu53G59 7ejS9YoyQMS7W8lw+aMqJhrUA9CIeQ6S+qvoZ8g70DOLWiQS1W02iRVxXPqMDvkWUM ckkspk1ImpajA== Date: Mon, 16 Feb 2026 10:11:08 -0800 From: Jakub Kicinski To: Eric Dumazet Cc: kuniyu@google.com, ncardwell@google.com, netdev@vger.kernel.org, davem@davemloft.net, pabeni@redhat.com, andrew+netdev@lunn.ch, horms@kernel.org Subject: Re: [PATCH net-next] tcp: try to defer / return acked skbs to originating CPU Message-ID: <20260216101108.6b2319b2@kernel.org> In-Reply-To: References: <20260117164255.785751-1-kuba@kernel.org> <20260117150346.72265ac3@kernel.org> <20260119090435.44b1da2d@kernel.org> <20260129150459.29419003@kernel.org> <20260216094936.5bf9d789@kernel.org> 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-Transfer-Encoding: 7bit On Mon, 16 Feb 2026 18:58:08 +0100 Eric Dumazet wrote: > > > I think I totally missed your email :/ > > > > > > What about not attempting defer for zero copy skbs ? > > > > > > It turns out existing patch e20dfbad8aab ("net: fix napi_consume_skb() > > > with alien skbs") is already a problem for zcopy. > > > > We definitely need either this or the timer patch I attached, for UDP. > > > > I put the TCP write side on a back burner because slab sheaves got > > merged, I think skb defer free will still make a difference but IDK > > how much. Maybe juice will no longer be worth the squeeze? > > It depends how many frags are attached to each skb. > > page frags are not yet handled by SLUB sheaves :) Ack, my recollection is that more of the cycles are spent in slab than pcp handling, tho. I could be misremembering. But my thinking was that if we both: - lose zc sends due to the unbounded completion time - lose the slab benefit due to sheaves we are only left with fairly narrow case of page handling of small skbs. My gut feeling was that however unclean the timer fix would be best since it gives us zc back. But I don't have a way to experiment with sheaves yet to get data. All of this is pure speculation. Regardless the patch you shared earlier is probably best as a fix for zero-copy UDP for now.