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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 67D1AC433F5 for ; Thu, 30 Sep 2021 16:30:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4F5B861250 for ; Thu, 30 Sep 2021 16:30:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1351403AbhI3QcT (ORCPT ); Thu, 30 Sep 2021 12:32:19 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:35977 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1351345AbhI3QcK (ORCPT ); Thu, 30 Sep 2021 12:32:10 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1633019426; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=u7/zMdrPeVyZNLTntHruwDpYub+H9qwtzzzSUntktcA=; b=Y3+XlroLA5TtOUcqWUR5haHikw0SJVLqBzWXn5InZ2zgRSGgjZ2tTrBMRs4HcGyGb0AWFM ofLQ+LtiGFkzEOtJgCm/NvDetOHnxxp46whs0VsIoXWO1hKgY8AKWIpvGN0R2qIFzkRu11 x/yu/UMVRMAiC+d7an5WpDsYSHJaU28= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-505-z2r_DDwdMRWSxVzVoPhJUw-1; Thu, 30 Sep 2021 12:30:22 -0400 X-MC-Unique: z2r_DDwdMRWSxVzVoPhJUw-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 3FA3A18125C0; Thu, 30 Sep 2021 16:30:19 +0000 (UTC) Received: from localhost (unknown [10.39.195.132]) by smtp.corp.redhat.com (Postfix) with ESMTP id A3A2B1017E3E; Thu, 30 Sep 2021 16:30:18 +0000 (UTC) Date: Thu, 30 Sep 2021 17:30:17 +0100 From: Stefan Hajnoczi To: Andy Lutomirski Cc: Sohil Mehta , the arch/x86 maintainers , Tony Luck , Dave Hansen , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Jens Axboe , Christian Brauner , "Peter Zijlstra (Intel)" , Shuah Khan , Arnd Bergmann , Jonathan Corbet , Raj Ashok , Jacob Pan , Gayatri Kammela , Zeng Guang , "Williams, Dan J" , Randy E Witt , "Shankar, Ravi V" , Ramesh Thomas , Linux API , linux-arch@vger.kernel.org, Linux Kernel Mailing List , 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> <456bf9cf-87b8-4c3d-ac0c-7e392bcf26de@www.fastmail.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="IzEoHzzIxT1o87/+" Content-Disposition: inline In-Reply-To: <456bf9cf-87b8-4c3d-ac0c-7e392bcf26de@www.fastmail.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --IzEoHzzIxT1o87/+ Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Sep 28, 2021 at 09:31:34PM -0700, Andy Lutomirski wrote: > On Mon, Sep 13, 2021, at 1:01 PM, Sohil Mehta wrote: > > User Interrupts Introduction > > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D > > > > User Interrupts (Uintr) is a hardware technology that enables delivering > > interrupts directly to user space. > > > > Today, virtually all communication across privilege boundaries happens = by going > > through the kernel. These include signals, pipes, remote procedure call= s and > > hardware interrupt based notifications. User interrupts provide the fou= ndation > > for more efficient (low latency and low CPU utilization) versions of th= ese > > common operations by avoiding transitions through the kernel. > > >=20 > ... >=20 > I spent some time reviewing the docs (ISE) and contemplating how this all= fits together, and I have a high level question: >=20 > Can someone give an example of a realistic workload that would benefit fr= om SENDUIPI and precisely how it would use SENDUIPI? Or an example of a re= alistic workload that would benefit from hypothetical device-initiated user= interrupts and how it would use them? I'm having trouble imagining someth= ing that wouldn't work as well or better by simply polling, at least on DMA= -coherent architectures like x86. I was wondering the same thing. One thing came to mind: An application that wants to be *interrupted* from what it's doing rather than waiting until the next polling point. For example, applications that are CPU-intensive and have green threads. I can't name a real application like this though :P. Stefan --IzEoHzzIxT1o87/+ Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAmFV5hkACgkQnKSrs4Gr c8gkYAf8DF5mZAyvdq7MYNw7V3LLjLXQA/PJX65e9s/VzX1DOImgxepjEQfAkQUT /IncDgMu0mkE0+jU/ZwEngFzI77d5uDzt/xV8cVHjqfE7vCy8SASNg4HFijkl7aF aS+vZ2XK89S28S8ocQ/d7GPE80E+IEuxjInzASwimHFCmFtW8U+ka4CmIxbsw6e1 1ahYfTSnKrwSR2qSzW7cwU4WZFibG0TR0Lgz/oBm9dQuqu7IArWmSTNRKAQPJtqU Q+TtjQh/s1Gvvzq8gvdBB6/2mWVE4fUfwatayUBb3HdcUt+5/J32kT/vjeY9HSZL PkwYaTLC72ly4H9nhy2lYDD7XbfgFQ== =O0C0 -----END PGP SIGNATURE----- --IzEoHzzIxT1o87/+--