From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH v2] arm/arm64: KVM: Properly account for guest CPU time Date: Mon, 01 Jun 2015 13:52:18 +0200 Message-ID: <556C4772.1070506@redhat.com> References: <1432838950-28774-1-git-send-email-christoffer.dall@linaro.org> <556C0E22.9090401@de.ibm.com> <556C435D.3050900@redhat.com> <556C4510.80704@de.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Transfer-Encoding: 7bit Cc: Marc Zyngier To: Christian Borntraeger , Christoffer Dall , kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org Return-path: Received: from mx1.redhat.com ([209.132.183.28]:60762 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751422AbbFALwX (ORCPT ); Mon, 1 Jun 2015 07:52:23 -0400 In-Reply-To: <556C4510.80704@de.ibm.com> Sender: kvm-owner@vger.kernel.org List-ID: On 01/06/2015 13:42, Christian Borntraeger wrote: > Am 01.06.2015 um 13:34 schrieb Paolo Bonzini: >> >> >> On 01/06/2015 09:47, Christian Borntraeger wrote: >>> >>> 1: "disable", "guest", "disable again and save", "restore to disable", "enable" >>> and now it is >>> 2: "disable", "guest", "enable" >>> and with your patch it is >>> 3: "disable", "guest", "enable", "disable, "enable" >>> >>> I assume that 3 and 1 are similar in its costs, so this is probably ok. >> >> At least on x86, 3 and 2 are similar, but 3 is much more expensive than >> 1! See https://lkml.org/lkml/2015/5/5/835: > > That does not make sense. If 3 and 2 are similar, then 2 must be much more > expensive than 1 as well. As 2 is a strict subset of 1 it must be cheaper, no? Yes, it must. I meant 3 is much cheaper than 1. Paolo >> Cost of: CLI insn same-IF : 0 cycles >> Cost of: CLI insn flip-IF : 0 cycles >> Cost of: STI insn same-IF : 0 cycles >> Cost of: STI insn flip-IF : 0 cycles >> Cost of: PUSHF insn : 0 cycles >> Cost of: POPF insn same-IF : 20 cycles >> Cost of: POPF insn flip-IF : 28 cycles >> Cost of: local_irq_save() fn : 20 cycles >> Cost of: local_irq_restore() fn same-IF : 24 cycles >> Cost of: local_irq_restore() fn flip-IF : 28 cycles >> Cost of: irq_save()+restore() fn same-IF : 48 cycles >> Cost of: irq_save()+restore() fn flip-IF : 48 cycles > > Yes its similar on s390. local_irq_save/restore is noticable in guest exit > hot loops (thats what inspired my patch), but a simple irq disable is > just single cycle pipelined. Given the design of aggressive out-out order > designs with all the architectural ordering this makes sense. > > Christian >