From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A74F3C433EF for ; Thu, 23 Sep 2021 12:19:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8E45961214 for ; Thu, 23 Sep 2021 12:19:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240882AbhIWMUu (ORCPT ); Thu, 23 Sep 2021 08:20:50 -0400 Received: from mail.kernel.org ([198.145.29.99]:44976 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240987AbhIWMUj (ORCPT ); Thu, 23 Sep 2021 08:20:39 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id A753361214; Thu, 23 Sep 2021 12:19:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1632399548; bh=a5drWzuoeMZl8QP24M3+/zzD9bz02p+umQKMUtGw/us=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=I/mTuHbo2gLcg9kkEvmFogd2VA8vMY06o9QjuRssvz5ca5X16E29nSfJHjVqYlvON AAjPv2xjDCwOnqOjTatbJGebL91RmGSqgVKwn6ouKN9V1zudAfAOoY4XWPISHnNaeP fx3vOX8EQqw7aGWb5n8vm1/D/l0XNWiftPVdmBmU= Date: Thu, 23 Sep 2021 14:19:05 +0200 From: Greg KH To: "Mehta, Sohil" Cc: "Hansen, Dave" , "x86@kernel.org" , "linux-kernel@vger.kernel.org" , "Luck, Tony" , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H . Peter Anvin" , "Lutomirski, Andy" , Jens Axboe , Christian Brauner , Peter Zijlstra , Shuah Khan , Arnd Bergmann , Jonathan Corbet , "Raj, Ashok" , Jacob Pan , "Kammela, Gayatri" , "Zeng, Guang" , "Williams, Dan J" , "Witt, Randy E" , "Shankar, Ravi V" , "Thomas, Ramesh" , "linux-api@vger.kernel.org" , "linux-arch@vger.kernel.org" , "linux-kselftest@vger.kernel.org" Subject: Re: [RFC PATCH 00/13] x86 User Interrupts support Message-ID: References: <20210913200132.3396598-1-sohil.mehta@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 14, 2021 at 07:03:36PM +0000, Mehta, Sohil wrote: > Resending.. There were some email delivery issues. > > On 9/13/2021 1:27 PM, Dave Hansen wrote: > > User Interrupts directly deliver events to user space and are > > 10x faster than the closest alternative. > > Thanks Dave. This is definitely more attention-grabbing than the > previous intro. I'll include this next time. > > One thing to note, the 10x gain is only applicable for User IPIs. > For other source of User Interrupts (like kernel-to-user > notifications and other external sources), we don't have the data > yet. > > I realized the User IPI data in the cover also needs some > clarification. The 10x gain is only seen when the receiver is > spinning in User space - waiting for interrupts. > > If the receiver were to block (wait) in the kernel, the performance > would drop as expected. However, User IPI (blocked) would still be > 10% faster than Eventfd and 40% faster than signals. > > Here is the updated table: > +---------------------+-------------------------+ > | IPC type | Relative Latency | > | |(normalized to User IPI) | > +---------------------+-------------------------+ > | User IPI | 1.0 | > | User IPI (blocked) | 8.9 | > | Signal | 14.8 | > | Eventfd | 9.7 | > | Pipe | 16.3 | > | Domain | 17.3 | > +---------------------+-------------------------+ Relative is just that, "relative". If the real values are extremely tiny, then relative is just "this goes a tiny tiny bit faster than what you have today in eventfd", right? So how about "absolute"? What are we talking here? And this is really only for the "one userspace task waking up another userspace task" policies. What real workload can actually use this? thanks, greg k-h