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 F40C515C8; Wed, 28 Feb 2024 15:35:46 +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=1709134547; cv=none; b=DQWT9cJAB8zQaNkHNPtiQ/TRpl8O1gzAc+QkDKiibobV3ryjcRD5UxJEU/6/bhF48ns0+hoa2iBPHiI7DcBDlSeh0Kp/0m7PPIyfOM3eO44t3WlSAAtuTzbNSl2rL/h1TIZ20lSByCLmzdMCluDkmsox3ChNkbZ5DuREBJo6Rgw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1709134547; c=relaxed/simple; bh=Ow0oMcjP9WmZsxfrrSXHg6DV3yhPxuTY7U/vGkGDAk0=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=csgnzSLVlTTcb1Cv+erbMmfOX7wxqGgzghGR5/J9/r/VvstR/b82kBRGMWVQzmawsGCmGSbEI3tdHugdlJ4rHj1kXdMKtPhX1Z9Uihh6vPPDNGXH1vb3CWYGIDgk0KUOVD90hyXZ9ReMv4Siy0z9zzz1ztOyHhcmCtHWz8tE3Tk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=FjYMzDmK; 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="FjYMzDmK" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C5059C433F1; Wed, 28 Feb 2024 15:35:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1709134546; bh=Ow0oMcjP9WmZsxfrrSXHg6DV3yhPxuTY7U/vGkGDAk0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=FjYMzDmK0IQosaEYUJyTURCigp714oQKlOA4XW/fr2d9wr8GLnE6+YlOaCtrPYr1/ AyLRbs5tT5JQu/HwctS/gctasVnVJVwXuGXeNTZnQjvTSTVZxVag3mZtDxGNxs5tti HmO7dNDqYzNRe5oVx2/Wtvw/5/yy063g8AaLRgn6a7mnCM7uFY0PPePV2OEQr9gynR AP9mR9vW4/PRniAk3bZ5mzZ/3b9uZEfqnM+4y5hd14dPnqEReYjWItA7iW22h1JKcO zOGRGtY00+x1vHsKfvKN1RCp84agHNXre1rxFBqKwGFIE0J60FVW3dJnZkw9O85OC+ iRT5HPXD8FyiA== Date: Wed, 28 Feb 2024 07:35:44 -0800 From: Jakub Kicinski To: "Paul E. McKenney" Cc: Eric Dumazet , Yan Zhai , netdev@vger.kernel.org, "David S. Miller" , Paolo Abeni , Jiri Pirko , Simon Horman , Daniel Borkmann , Lorenzo Bianconi , Coco Li , Wei Wang , Alexander Duyck , Hannes Frederic Sowa , linux-kernel@vger.kernel.org, rcu@vger.kernel.org, bpf@vger.kernel.org, kernel-team@cloudflare.com Subject: Re: [PATCH] net: raise RCU qs after each threaded NAPI poll Message-ID: <20240228073544.791ae897@kernel.org> In-Reply-To: <9a0052f9-b022-42c9-a5da-1d6ca3b00885@paulmck-laptop> References: <20240227191001.0c521b03@kernel.org> <66a81295-ab6f-41f4-a3da-8b5003634c6a@paulmck-laptop> <20240228064343.578a5363@kernel.org> <9a0052f9-b022-42c9-a5da-1d6ca3b00885@paulmck-laptop> Precedence: bulk X-Mailing-List: linux-kernel@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 Wed, 28 Feb 2024 07:15:42 -0800 Paul E. McKenney wrote: > > > Another complication is that although CONFIG_PREEMPT_RT kernels are > > > built with CONFIG_PREEMPT_RCU, the reverse is not always the case. > > > And if we are not repolling, don't we have a high probability of doing > > > a voluntary context when we reach napi_thread_wait() at the beginning > > > of that loop? > > > > Very much so, which is why adding the cost of rcu_softirq_qs() > > for every NAPI run feels like an overkill. > > Would it be better to do the rcu_softirq_qs() only once every 1000 times > or some such? Or once every HZ jiffies? > > Or is there a better way? Right, we can do that. Yan Zhai, have you measured the performance impact / time spent in the call?