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Wed, 15 Jan 2020 13:50:58 +0000 MIME-Version: 1.0 Date: Wed, 15 Jan 2020 13:50:58 +0000 From: Marc Zyngier To: Shaokun Zhang Subject: Re: [Question about KVM on arm64] Consider putting VINVALL to deactivation In-Reply-To: References: Message-ID: <37126a877e1160ed50ee6d95a03d1574@kernel.org> X-Sender: maz@kernel.org User-Agent: Roundcube Webmail/1.3.8 X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: zhangshaokun@hisilicon.com, tangnianyao@huawei.com, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, fanhenglong@huawei.com, wanghaibin.wang@huawei.com, lizixian@hisilicon.com, wangwudi@hisilicon.com, jiayanlei@huawei.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200115_055101_777533_C32F0C98 X-CRM114-Status: GOOD ( 12.10 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: wangwudi , Lizixian , jiayanlei@huawei.com, fanhenglong@huawei.com, "Tangnianyao \(ICT\)" , wanghaibin.wang@huawei.com, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Shaokun, On 2020-01-14 14:20, Shaokun Zhang wrote: > Hi Marc, > > On activation, VMAPP command is followed by a VINVALL, which could be > quite expensive for the start-up of virtual machine. If a vpeid is > allowed > successfully, it is not used in system. How expensive? This is exactly similar to what happens on a physical machine where we perform an INVALL on MAPC. And yet you don't complain about that. Please provide numbers. > We may consider put VINVALL to deactivation to ensure all cache of > certain > vpeid is invalid, to simplify activation. We consider start-up may be > more > common and more time-consuming-sensitive than shutdown process. In my world, they cost the same thing, and happen just as often. Also, I want guarantees that on VMAPP, there is no stale information even if this is the first time we're using this VPEid (who knows what happens over kexec, for example). > Do you think it's all right? I don't, for the reasons stated above. You also provide no numbers showing how bad the overhead is, so I'm left guessing. Thanks, M. -- Jazz is not dead. It just smells funny... _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel