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Thu, 17 Sep 2020 11:21:17 +0100 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Thu, 17 Sep 2020 11:21:15 +0100 From: Marc Zyngier To: Leo Yan Cc: Sergey Senozhatsky , Arnaldo Carvalho de Melo , Mark Rutland , Peter Zijlstra , Will Deacon , John Garry , Mathieu Poirier , Namhyung Kim , Suleiman Souhlal , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCHv3] perf kvm: add kvm-stat for arm64 In-Reply-To: <20200917101219.GD12548@leoy-ThinkPad-X240s> References: <20200917003645.689665-1-sergey.senozhatsky@gmail.com> <20200917100950.GC12548@leoy-ThinkPad-X240s> <20200917101219.GD12548@leoy-ThinkPad-X240s> User-Agent: Roundcube Webmail/1.4.8 Message-ID: <652f10660f09bd608b825233713f775a@kernel.org> X-Sender: maz@kernel.org X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: leo.yan@linaro.org, sergey.senozhatsky@gmail.com, acme@kernel.org, mark.rutland@arm.com, peterz@infradead.org, will@kernel.org, john.garry@huawei.com, mathieu.poirier@linaro.org, namhyung@kernel.org, suleiman@google.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-09-17 11:12, Leo Yan wrote: > Add Marc at this time, sorry for spamming. > > On Thu, Sep 17, 2020 at 06:09:50PM +0800, Leo Yan wrote: >> [ + Marc ] >> >> On Thu, Sep 17, 2020 at 09:36:45AM +0900, Sergey Senozhatsky wrote: >> >> [...] >> >> > diff --git a/tools/perf/arch/arm64/util/kvm-stat.c b/tools/perf/arch/arm64/util/kvm-stat.c >> > new file mode 100644 >> > index 000000000000..32e58576f186 >> > --- /dev/null >> > +++ b/tools/perf/arch/arm64/util/kvm-stat.c >> > @@ -0,0 +1,86 @@ >> > +// SPDX-License-Identifier: GPL-2.0 >> > +#include >> > +#include >> > +#include "../../util/evsel.h" >> > +#include "../../util/kvm-stat.h" >> > +#include "arm64_exception_types.h" >> > +#include "debug.h" >> > + >> > +define_exit_reasons_table(arm64_exit_reasons, kvm_arm_exception_type); >> > +define_exit_reasons_table(arm64_trap_exit_reasons, kvm_arm_exception_class); >> > + >> > +const char *kvm_trap_exit_reason = "esr_ec"; >> > +const char *vcpu_id_str = "id"; >> >> On Arm64, ftrace tracepoint "kvm_entry" doesn't contain the field "id" >> or field "vcpu_id", thus it always reads out the "id" is 0 and it is >> recorded into Perf's structure vcpu_event_record::vcpu_id and assigned >> to perf thread's private data "thread::private". >> >> With current code, it will not mess up different vcpus' samples >> because >> now the samples are analyzed based on thread context, but since all >> threads' "vcpu_id" is zero, thus all samples are accounted for >> "vcpu_id=0" and cannot print out correct result with option "--vcpu": >> >> >> $ perf kvm stat report --vcpu 4 >> >> Analyze events for all VMs, VCPU 4: >> >> VM-EXIT Samples Samples% Time% Min Time Max >> Time Avg time >> >> Total Samples:0, Total events handled time:0.00us. >> >> >> This is an issue I observed, if we want to support option "--vcpu", >> seems we need to change ftrace event for "kvm_entry", but this will >> break ABI. >> >> Essentially, this issue is caused by different archs using different >> format for ftrace event "kvm_entry", on x86 it contains feild >> "vcpu_id" but arm64 only just records "vcpu_pc". >> >> @Marc, @Will, do you have any suggestion for this? Do you think it's >> feasible to add a new field "vcpu_id" into the tracepoint "kvm_entry" >> for Arm64's version? The question really is: how will you handle the ABI breackage? I don't see a good solution for it, apart from having a *separate* tracepoint that collects all the information you need. And even that is really ugly. M. -- Jazz is not dead. It just smells funny...