From nobody Tue May 7 19:51:29 2024 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) client-ip=208.118.235.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Authentication-Results: mx.zohomail.com; spf=pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org Return-Path: Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) by mx.zohomail.com with SMTPS id 15053136641331005.7845489844917; Wed, 13 Sep 2017 07:41:04 -0700 (PDT) Received: from localhost ([::1]:42893 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ds8qd-0003ZE-9N for importer@patchew.org; Wed, 13 Sep 2017 10:41:03 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43198) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ds8po-0003AT-J5 for qemu-devel@nongnu.org; Wed, 13 Sep 2017 10:40:13 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ds8pj-0001Mq-2S for qemu-devel@nongnu.org; Wed, 13 Sep 2017 10:40:12 -0400 Received: from mx2.suse.de ([195.135.220.15]:35552 helo=mx1.suse.de) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1ds8pi-0001Lf-S7 for qemu-devel@nongnu.org; Wed, 13 Sep 2017 10:40:07 -0400 Received: from relay1.suse.de (charybdis-ext.suse.de [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 41D66AB1E; Wed, 13 Sep 2017 14:40:03 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de From: Alexander Graf To: qemu-devel@nongnu.org Date: Wed, 13 Sep 2017 16:39:58 +0200 Message-Id: <20170913143958.86385-1-agraf@suse.de> X-Mailer: git-send-email 2.12.3 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x (no timestamps) [generic] [fuzzy] X-Received-From: 195.135.220.15 Subject: [Qemu-devel] [PATCH] target-i386: enable kvm_pv_unhalt by default X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Paolo Bonzini , Andrew Jones , Eduardo Habkost , =?UTF-8?q?Andreas=20F=C3=A4rber?= , Richard Henderson Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail: RSF_0 Z_629925259 SPT_0 Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Commit f010bc643a (target-i386: add feature kvm_pv_unhalt) introduced the kvm_pv_unhalt feature but didn't enable it by default. Without kvm_pv_unhalt we see a measurable degradation in scheduling performance, so enabling it by default does make sense IMHO. This patch just flips it to default to on by default. [With kvm_pv_unhalt disabled] $ perf bench sched messaging -l 10000 Total time: 8.573 [sec] [With kvm_pv_unhalt enabled] $ perf bench sched messaging -l 10000 Total time: 4.416 [sec] Signed-off-by: Alexander Graf --- Let's ask everyone who was involved back then whether this is a feature that is good to enable by default. My measurements imply so, but who knows.= .. Also, I'd kindly like to ask for guidance on how to make this reasonably well backwards compatible. I assume we only want to flip the default in new= er machine models? If so, how? --- target/i386/cpu.c | 1 + 1 file changed, 1 insertion(+) diff --git a/target/i386/cpu.c b/target/i386/cpu.c index 69676e13e1..c58f4ab24f 100644 --- a/target/i386/cpu.c +++ b/target/i386/cpu.c @@ -1581,6 +1581,7 @@ static PropValue kvm_default_props[] =3D { { "kvm-asyncpf", "on" }, { "kvm-steal-time", "on" }, { "kvm-pv-eoi", "on" }, + { "kvm-pv-unhalt", "on" }, { "kvmclock-stable-bit", "on" }, { "x2apic", "on" }, { "acpi", "off" }, --=20 2.12.3