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Linux aarch64; rv:60.0) Gecko/20100101 Thunderbird/60.3.1 MIME-Version: 1.0 In-Reply-To: <20190108120352.GN10769@e113682-lin.lund.arm.com> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190108_041219_106879_58C453C7 X-CRM114-Status: GOOD ( 21.82 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Julien Thierry , Catalin Marinas , joro@8bytes.org, Suzuki K Poulose , Will Deacon , Andrew Murray , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 08/01/2019 12:03, Christoffer Dall wrote: > On Tue, Jan 08, 2019 at 11:50:59AM +0000, Marc Zyngier wrote: >> On Tue, 08 Jan 2019 11:25:13 +0000, >> Andrew Murray wrote: >> >> Hi Andrew, >> >>> My only doubt about this is as follows. If, on a KVM host you run this: >>> >>> perf stat -e cycles:H lkvm run ... >>> >>> then on the VHE host the cycles reported represents the entire non-guest cycles >>> associated with running the guest. >>> >>> On a !VHE, the cycles reported exclude EL2 (with or without this patch) and >>> thus you don't get a representation of all the non-guest cycles associated with >>> the guest. However without this patch you could at least still run: >>> >>> perf stat -e cycles:H -e cycles:h lkvm run ... >>> >>> and then add the two cycle counts together to get something comparative with >>> the VHE host. >>> >>> If the above patch represents the desired semantics, then perhaps we must count >>> both EL1 and *EL2* for !exclude_kernel on !VHE. In fact I think we should do >>> this anyway and remove a little complexity from armv8pmu_set_event_filter. >>> Thoughts? >> >> I'm not sure we should hide the architectural differences between VHE >> and !VHE. If you're trying to measure what is happening at in the >> hypervisor, you can't reason about it while ignoring the dual nature >> of !VHE. >> > > How do you define hypervisor here? Is that just the code that runs at > EL2 or also parts of KVM that runs at EL1? I define it as "not a guest". Whatever is used to support a guest is the hypervisor. > It remains unclear to me why you'd want to measure a subset of KVM, > which happens to run in EL2, in your host (and hypervisor-enabled) > kernel, and you are even precluded from measuring a comparable portion > of your implementation on other Arm systems (VHE). Because I'm not trying to compare apples (VHE) and oranges (!VHE). My use-case for perf is to measure the impact of a change on a given implementation, and the more I can narrow the impact of that change, the better (specially when !VHE precludes the use of other techniques such as sampling). > Admittedly, I'm not at export in using perf, but I find this EL1/EL2 > distinction out of place as it relates to exlude_kernel, exlude_user, > and exlude_hv. Will we have a fourth Arm-specific flag which takes the > place of exclude_hv on PowerPC, which excludes an underlying hypervisor > when running a guest, should we ever support counting that in the > future? In all honestly, exclude_hv doesn't make much sense to me on a VHE system, unless you define an arbitrary cutting point where things are on one side or the other. As for a fourth flag, I have no idea. 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