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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 994F1ECDFB8 for ; Fri, 20 Jul 2018 09:51:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4A69A20652 for ; Fri, 20 Jul 2018 09:51:42 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4A69A20652 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728153AbeGTKjG (ORCPT ); Fri, 20 Jul 2018 06:39:06 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:36374 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727321AbeGTKjG (ORCPT ); Fri, 20 Jul 2018 06:39:06 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id DA2938182D0F; Fri, 20 Jul 2018 09:51:38 +0000 (UTC) Received: from flask (unknown [10.43.2.80]) by smtp.corp.redhat.com (Postfix) with SMTP id E3FE32142F20; Fri, 20 Jul 2018 09:51:36 +0000 (UTC) Received: by flask (sSMTP sendmail emulation); Fri, 20 Jul 2018 11:51:36 +0200 Date: Fri, 20 Jul 2018 11:51:36 +0200 From: Radim Krcmar To: Wanpeng Li Cc: LKML , kvm , Paolo Bonzini , Vitaly Kuznetsov Subject: Re: [PATCH v3 2/6] KVM: X86: Implement PV IPIs in linux guest Message-ID: <20180720095135.GA8330@flask> References: <1530598891-21370-1-git-send-email-wanpengli@tencent.com> <1530598891-21370-3-git-send-email-wanpengli@tencent.com> <20180719162826.GB11749@flask> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.8]); Fri, 20 Jul 2018 09:51:38 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.8]); Fri, 20 Jul 2018 09:51:38 +0000 (UTC) for IP:'10.11.54.6' DOMAIN:'int-mx06.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'rkrcmar@redhat.com' RCPT:'' Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2018-07-20 11:33+0800, Wanpeng Li: > On Fri, 20 Jul 2018 at 00:28, Radim Krčmář wrote: > > 2018-07-03 14:21+0800, Wanpeng Li: > > But because it is very similar to x2apic, I'd really need some real > > performance data to see if this benefits a real workload. > > Thanks for your review, Radim! :) I will find another real benchmark > instead of the micro one to evaluate the performance. Analyzing the cpu bitmap for every IPI request on a non-small guest (at least 32 VCPUs, ideally >256) during various workloads could also provide some insight regardless of workload/benchmark result -- we want to know how many VM exits we would save. > > > +static void kvm_send_ipi_all(int vector) > > > +{ > > > + __send_ipi_mask(cpu_online_mask, vector); > > > > These should be faster when using the native APIC shorthand -- is this > > the "Broadcast" in your tests? > > Not true, .send_IPI_all almost no callers though linux apic drivers > implement this hook, in addition, shortcut is not used for x2apic > mode(__x2apic_send_IPI_dest()), and very limited using in other > scenarios according to linux apic drivers. Good point, (xAPIC is using shorthands, so I didn't expect we'd stop doing so on x2APIC, but there was probably no need.) thanks.