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=-0.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, 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 3B79CC34047 for ; Wed, 19 Feb 2020 10:37:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 078F424656 for ; Wed, 19 Feb 2020 10:37:13 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="Q3HPkrlI" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726558AbgBSKhJ (ORCPT ); Wed, 19 Feb 2020 05:37:09 -0500 Received: from mail-wm1-f48.google.com ([209.85.128.48]:54617 "EHLO mail-wm1-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726270AbgBSKhJ (ORCPT ); Wed, 19 Feb 2020 05:37:09 -0500 Received: by mail-wm1-f48.google.com with SMTP id n3so17621wmk.4; Wed, 19 Feb 2020 02:37:07 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=YR8HyDW/1JEJwc8Sq5lAsfNmZdjey8txPG9y+rKXtEo=; b=Q3HPkrlIVqTM5/ph1qsmWRZI8SRyEQ4JRj7tXLmq4B548T01sn2x6P9Rw6eneQW2MI o3xauSlYv17dtcUAuY/Me0JncmDhAUgtFPsXWfaT1pgYc2Zn5IAzoxoRbYitXLn02OAm InoxsdZPJcS7FrJHFrKOEaJM/mzWhSRUXQ/QF9X4yoUAGMECT/vapvXYJPegg9SLfCN8 DOfjHO1/5r4aDELgQY2z21kZAZX1+UmK9oQBS2g4RIzEHmAxyx5CR3vvunaEn6MgXtfR h/LsSvB+WcjP1hJBj7MQJ2AieSKcufViVILUsWZVyFBnD5cT1m6w+NPzXUegVOlt6LdE 2gQQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=YR8HyDW/1JEJwc8Sq5lAsfNmZdjey8txPG9y+rKXtEo=; b=Gk9qFRB0RD9mYxNqxoPKu8wWsoqsDh/dsf2vSwjfCKn3U/rlIYL1nXeracaBo1zJna YSYt1SHWh4jbtlpjURXccXijIXFC7KqEON4FZqjLzRN/SdLGOsx8CihC6heSxU5XqRI6 ubZOyGuOeqO3TNq2mrpmAoKUsq8shxJZGPYaDT4hE8ISyUNJZp68NEAB+tkhNb+YD26T xNgugnYPzmgevNR6D5k86W4ulrH3L0jDRS7G3sGVVUgAlxTBGOvQVRoAzHgr2XPMIiH3 OpIJet3RspQWnOijdRPvbT94hA5n591PjWPLMC+jGI+BIgLFgPl2Hehs09U8NeAbyzCg P2QA== X-Gm-Message-State: APjAAAUtAsyWcPAD0gx1YYNDHEaTnmCTf7iYMLX+5bZeGLAT+FVldyIV UXr896OdapXbmOo9KQIiyO/KY+olQcE= X-Google-Smtp-Source: APXvYqxzNgICRLz31TuNCbiNHXiNhH0Lyu27oebKWdTKttePk1LwZrftmpiEAUwwZ9dt0dR5LM8CXQ== X-Received: by 2002:a7b:c778:: with SMTP id x24mr3735887wmk.115.1582108626841; Wed, 19 Feb 2020 02:37:06 -0800 (PST) Received: from localhost ([51.15.41.238]) by smtp.gmail.com with ESMTPSA id d22sm2297956wmd.39.2020.02.19.02.37.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 19 Feb 2020 02:37:05 -0800 (PST) Date: Wed, 19 Feb 2020 10:37:04 +0000 From: Stefan Hajnoczi To: Avi Kivity Cc: Paolo Bonzini , Stefan Hajnoczi , linux-fsdevel@vger.kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Davide Libenzi , Alexander Viro Subject: Re: [RFC] eventfd: add EFD_AUTORESET flag Message-ID: <20200219103704.GA1076032@stefanha-x1.localdomain> References: <20200129172010.162215-1-stefanha@redhat.com> <66566792-58a4-bf65-6723-7d2887c84160@redhat.com> <20200212102912.GA464050@stefanha-x1.localdomain> <156cb709-282a-ddb6-6f34-82b4bb211f73@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="bp/iNruPH9dso1Pn" Content-Disposition: inline In-Reply-To: Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org --bp/iNruPH9dso1Pn Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Feb 12, 2020 at 12:54:30PM +0200, Avi Kivity wrote: >=20 > On 12/02/2020 12.47, Paolo Bonzini wrote: > > On 12/02/20 11:29, Stefan Hajnoczi wrote: > > > On Wed, Feb 12, 2020 at 09:31:32AM +0100, Paolo Bonzini wrote: > > > > On 29/01/20 18:20, Stefan Hajnoczi wrote: > > > > > + /* Semaphore semantics don't make sense when autoreset is enabl= ed */ > > > > > + if ((flags & EFD_SEMAPHORE) && (flags & EFD_AUTORESET)) > > > > > + return -EINVAL; > > > > > + > > > > I think they do, you just want to subtract 1 instead of setting the > > > > count to 0. This way, writing 1 would be the post operation on the > > > > semaphore, while poll() would be the wait operation. > > > True! Then EFD_AUTORESET is not a fitting name. EFD_AUTOREAD or > > > EFD_POLL_READS? > > Avi's suggestion also makes sense. Switching the event loop from poll() > > to IORING_OP_POLL_ADD would be good on its own, and then you could make > > it use IORING_OP_READV for eventfds. > >=20 > > In QEMU parlance, perhaps you need a different abstraction than > > EventNotifier (let's call it WakeupNotifier) which would also use > > eventfd but it would provide a smaller API. Thanks to the smaller API, > > it would not need EFD_NONBLOCK, unlike the regular EventNotifier, and it > > could either set up a poll() handler calling read(), or use > > IORING_OP_READV when io_uring is in use. > >=20 >=20 > Just to be clear, for best performance don't use IORING_OP_POLL_ADD, just > IORING_OP_READ. That's what you say in the second paragraph but the first > can be misleading. Thanks, that's a nice idea! I already have experimental io_uring fd monitoring code written for QEMU and will extend it to use IORING_OP_READ. Stefan --bp/iNruPH9dso1Pn Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAl5ND9AACgkQnKSrs4Gr c8gMHAf/f9UuwAwjiMV/pwZZbwcYseAmnQ2FPZYE5HhiWScgJAg19otfE4JxYwR5 /NhXUNyYhp7sa0+fB+/aHJF/0mpIY70Mn1PX2umT7kb4ZpP6Qel0ZyVRuNOSp+k5 Wm19LAvKD4AyVu2Kxd4RJpibSu+UYelAT3Nh1d/c8Grrf0zHdcAj4Y4YwfTao1Xo kPgrIWGOPS7qxvS+fyg9ifT13LfhwFhpP3679AlOhUozQUrxnM77G8ehAOJQV8mS Ae+//m8fs/RVH2SRNgy7uRIr/v8pWdGt241pW8507oFHJChsRLFhNXJIWHP0dlUU xHILARbPURoXO+KG1YPtyO2Y+16cZQ== =5mbR -----END PGP SIGNATURE----- --bp/iNruPH9dso1Pn--