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=-8.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_2 autolearn=ham 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 910A6C2D0A3 for ; Wed, 4 Nov 2020 09:35:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DBDC6221F8 for ; Wed, 4 Nov 2020 09:35:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="XhHgJv3y" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728644AbgKDJfo (ORCPT ); Wed, 4 Nov 2020 04:35:44 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55652 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726691AbgKDJfn (ORCPT ); Wed, 4 Nov 2020 04:35:43 -0500 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 00D1FC0613D3; Wed, 4 Nov 2020 01:35:42 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=Mime-Version:Content-Type:References: In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=PgocQ7GiOOLpogLWmYicmur/hjgncbUmRV6ANwaJr1c=; b=XhHgJv3yYB0qDLBxJm0YRFjzz4 MEGAtGhYMkApEDNUKO9NDkMbRD2M6jOpkXLfAniv+VsxXip9fFRvXtoWCprFc+WysimVDBnYPd2nm Q8VAUopfw1we7QH0ppRTUPcYkgA4tg82XcdbHxUJ+qEAqnZGBhYC+FE9rEYnvdT/1EPktDLMgMy82 o8Yt22f7CUqveC/RlfOyWgXyBpQvaMgszciKGu2V8Y5k9ftgv/gTTREMfcusnnpmdGOwv8+q5Ail4 DXbwm0ZeDfbSIxlThevwgjQlPUup6zqnveu3QPchPYmfhdifeS6dpdmKilkXxZ+zRXnFfxrwyt4Dd oYls0YeQ==; Received: from 54-240-197-230.amazon.com ([54.240.197.230] helo=edge-cache-127.e-maa3.amazon.com) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kaFCd-0001vB-SG; Wed, 04 Nov 2020 09:35:40 +0000 Message-ID: Subject: Re: [PATCH v2 1/2] sched/wait: Add add_wait_queue_priority() From: David Woodhouse To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Paolo Bonzini , kvm@vger.kernel.org Date: Wed, 04 Nov 2020 09:35:37 +0000 In-Reply-To: <20201028143509.GA2628@hirez.programming.kicks-ass.net> References: <20201026175325.585623-1-dwmw2@infradead.org> <20201027143944.648769-1-dwmw2@infradead.org> <20201027143944.648769-2-dwmw2@infradead.org> <20201028143509.GA2628@hirez.programming.kicks-ass.net> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/x-pkcs7-signature"; boundary="=-3+1J5mr73iDK5ZVYir+8" X-Mailer: Evolution 3.28.5-0ubuntu0.18.04.2 Mime-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by merlin.infradead.org. See http://www.infradead.org/rpr.html Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --=-3+1J5mr73iDK5ZVYir+8 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, 2020-10-28 at 15:35 +0100, Peter Zijlstra wrote: > On Tue, Oct 27, 2020 at 02:39:43PM +0000, David Woodhouse wrote: > > From: David Woodhouse > >=20 > > This allows an exclusive wait_queue_entry to be added at the head of th= e > > queue, instead of the tail as normal. Thus, it gets to consume events > > first without allowing non-exclusive waiters to be woken at all. > >=20 > > The (first) intended use is for KVM IRQFD, which currently has > > inconsistent behaviour depending on whether posted interrupts are > > available or not. If they are, KVM will bypass the eventfd completely > > and deliver interrupts directly to the appropriate vCPU. If not, events > > are delivered through the eventfd and userspace will receive them when > > polling on the eventfd. > >=20 > > By using add_wait_queue_priority(), KVM will be able to consistently > > consume events within the kernel without accidentally exposing them > > to userspace when they're supposed to be bypassed. This, in turn, means > > that userspace doesn't have to jump through hoops to avoid listening > > on the erroneously noisy eventfd and injecting duplicate interrupts. > >=20 > > Signed-off-by: David Woodhouse >=20 > Acked-by: Peter Zijlstra (Intel) Thanks. Paolo, the conclusion was that you were going to take this set through the KVM tree, wasn't it? --=-3+1J5mr73iDK5ZVYir+8 Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCECow ggUcMIIEBKADAgECAhEA4rtJSHkq7AnpxKUY8ZlYZjANBgkqhkiG9w0BAQsFADCBlzELMAkGA1UE BhMCR0IxGzAZBgNVBAgTEkdyZWF0ZXIgTWFuY2hlc3RlcjEQMA4GA1UEBxMHU2FsZm9yZDEaMBgG A1UEChMRQ09NT0RPIENBIExpbWl0ZWQxPTA7BgNVBAMTNENPTU9ETyBSU0EgQ2xpZW50IEF1dGhl bnRpY2F0aW9uIGFuZCBTZWN1cmUgRW1haWwgQ0EwHhcNMTkwMTAyMDAwMDAwWhcNMjIwMTAxMjM1 OTU5WjAkMSIwIAYJKoZIhvcNAQkBFhNkd213MkBpbmZyYWRlYWQub3JnMIIBIjANBgkqhkiG9w0B AQEFAAOCAQ8AMIIBCgKCAQEAsv3wObLTCbUA7GJqKj9vHGf+Fa+tpkO+ZRVve9EpNsMsfXhvFpb8 RgL8vD+L133wK6csYoDU7zKiAo92FMUWaY1Hy6HqvVr9oevfTV3xhB5rQO1RHJoAfkvhy+wpjo7Q cXuzkOpibq2YurVStHAiGqAOMGMXhcVGqPuGhcVcVzVUjsvEzAV9Po9K2rpZ52FE4rDkpDK1pBK+ 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