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 E824C25A62E for ; Sat, 17 Jan 2026 17:10:11 +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=1768669812; cv=none; b=pIUJKz8Czmqh8jAxFOR1m4iLRGtAoENY+ZL/DojeO8u8q7ny2lPb7FR5CGIW9g/ZYvclD9tNrLLKZW6ou46glSLd5fgqAa7RYp8KYNALfeUOQENxKUH7covJCuMJ/1pLnFgee4Yt5rqX5UcDQQASotKWAJBQ3keV1Zli/6rgC0w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768669812; c=relaxed/simple; bh=TIbHV2TgW/OfrR6BMsysytWiYEp1aQCuA3ag7HA19sY=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=EAioabpgz0Qn1CgsJyY8Xsq3YdaotmP4VqgGe2lFDLlznn2SM0q57igH5rDwcftkhaWvxRUmHknXeU+1zcF6CjEkEupktCCCIXrQ4O+Hi/KdHbhexQx1EDkQyt76l+7rJCyq/R23aZSu3sHeSh2ikkbwPxebLQb16A3n1jae75A= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=KrX72Duu; 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="KrX72Duu" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EED76C4CEF7; Sat, 17 Jan 2026 17:10:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1768669811; bh=TIbHV2TgW/OfrR6BMsysytWiYEp1aQCuA3ag7HA19sY=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=KrX72DuuAQAJMXUeWAtFpIIdy65kIDKYS4sGWFK593aWs4LUixDtFr97EI2hnxo2F ffIwrk3C3PnDj8OxLjHE7IeQogMJleGIOvxVXFpoqogdH5QQTXe1UbwYT310BI3Aa2 Wnc42hdKy/XhkDAqj0e7FHSilDqO2RjyE/IdUAMcfzUF5byTuV6Q6RIxxNyPBws3Z5 jggIa28iEWtar+ZRJckq49AsYw1dD27gOzHF0ExTGc/UisEJ79xzBQTKsSzW6NmijE 1rhNaZnsJgb/cY4/DbVvkfX6JCg9nNK3x58vWtE3e3lUZpnCtIrPtJruDJwPYIR7iM L4lCcZb/drXTg== Date: Sat, 17 Jan 2026 09:10:10 -0800 From: Jakub Kicinski To: edumazet@google.com 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: <20260117091010.3133de3b@kernel.org> In-Reply-To: <20260117164255.785751-1-kuba@kernel.org> References: <20260117164255.785751-1-kuba@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 Sat, 17 Jan 2026 08:42:55 -0800 Jakub Kicinski wrote: > Running a memcache-like workload under production(ish) load > on a 300 thread AMD machine we see ~3% of CPU time spent > in kmem_cache_free() via tcp_ack(), freeing skbs from rtx queue. > This workloads pins workers away from softirq CPU so > the Tx skbs are pretty much always allocated on a different > CPU than where the ACKs arrive. Try to use the defer skb free > queue to return the skbs back to where they came from. > This results in a ~4% performance improvement for the workload. In the interest of full transparency the performance testing was done on a 6.13-ish kernel. But I don't see anything that'd make the situation better upstream..