From: Andi Kleen <ak@linux.intel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "Liang, Kan" <kan.liang@linux.intel.com>,
Luwei Kang <luwei.kang@intel.com>,
x86@kernel.org, linux-kernel@vger.kernel.org,
kvm@vger.kernel.org, mingo@redhat.com, acme@kernel.org,
mark.rutland@arm.com, alexander.shishkin@linux.intel.com,
jolsa@redhat.com, namhyung@kernel.org, tglx@linutronix.de,
bp@alien8.de, hpa@zytor.com, pbonzini@redhat.com,
sean.j.christopherson@intel.com, vkuznets@redhat.com,
wanpengli@tencent.com, jmattson@google.com, joro@8bytes.org,
pawan.kumar.gupta@linux.intel.com, thomas.lendacky@amd.com,
fenghua.yu@intel.com, like.xu@linux.intel.com
Subject: Re: [PATCH v1 01/11] perf/x86/core: Support KVM to assign a dedicated counter for guest PEBS
Date: Mon, 9 Mar 2020 08:44:45 -0700 [thread overview]
Message-ID: <20200309154445.GL1454533@tassilo.jf.intel.com> (raw)
In-Reply-To: <20200309100443.GG12561@hirez.programming.kicks-ass.net>
> Suppose your KVM thing claims counter 0/2 (ICL/SKL) for some random PEBS
> event, and then the host wants to use PREC_DIST.. Then one of them will
> be screwed for no reason what so ever.
It's no different from some user using an event that requires some
specific counter.
>
> How is that not destroying scheduling freedom? Any other situation we'd
> have moved the !PREC_DIST PEBS event to another counter.
Anyways what are you suggesting to do instead? Do you have a better proposal?
The only alternative I know to doing this would be to go through the PEBS
buffer in the guest and patch the applicable counter field up on each PMI.
I tried that at some point (still have code somewhere), but it was
quite complicated and tricky and somewhat slow, so I gave up eventually.
It's also inherently racy because if the guest starts looking at
the PEBS buffer before an PMI it could see the unpatched values
Given I don't know any real software which would break from this,
but such "polled PEBS" usages are certainly concievable.
The artificial constraint is a lot simpler and straight forward,
and also doesn't have any holes like this.
-Andi
next prev parent reply other threads:[~2020-03-09 15:44 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-05 17:56 [PATCH v1 00/11] PEBS virtualization enabling via DS Luwei Kang
2020-03-05 16:51 ` Paolo Bonzini
2020-03-05 17:56 ` [PATCH v1 01/11] perf/x86/core: Support KVM to assign a dedicated counter for guest PEBS Luwei Kang
2020-03-06 13:53 ` Peter Zijlstra
2020-03-06 14:42 ` Liang, Kan
2020-03-09 10:04 ` Peter Zijlstra
2020-03-09 13:12 ` Liang, Kan
2020-03-09 15:05 ` Peter Zijlstra
2020-03-09 19:28 ` Liang, Kan
2020-03-12 10:28 ` Kang, Luwei
2020-03-26 14:03 ` Liang, Kan
2020-04-07 12:34 ` Kang, Luwei
2020-06-12 5:28 ` Kang, Luwei
2020-06-19 9:30 ` Kang, Luwei
2020-08-20 3:32 ` Like Xu
2020-03-09 15:44 ` Andi Kleen [this message]
2020-03-05 17:56 ` [PATCH v1 02/11] perf/x86/ds: Handle guest PEBS events overflow and inject fake PMI Luwei Kang
2020-03-05 17:56 ` [PATCH v1 03/11] perf/x86: Expose a function to disable auto-reload Luwei Kang
2020-03-05 17:56 ` [PATCH v1 04/11] KVM: x86/pmu: Decouple event enablement from event creation Luwei Kang
2020-03-05 17:56 ` [PATCH v1 05/11] KVM: x86/pmu: Add support to reprogram PEBS event for guest counters Luwei Kang
2020-03-06 16:28 ` kbuild test robot
2020-03-09 0:58 ` Xu, Like
2020-03-05 17:57 ` [PATCH v1 06/11] KVM: x86/pmu: Implement is_pebs_via_ds_supported pmu ops Luwei Kang
2020-03-05 17:57 ` [PATCH v1 07/11] KVM: x86/pmu: Expose CPUIDs feature bits PDCM, DS, DTES64 Luwei Kang
2020-03-05 17:57 ` [PATCH v1 08/11] KVM: x86/pmu: PEBS MSRs emulation Luwei Kang
2020-03-05 17:57 ` [PATCH v1 09/11] KVM: x86/pmu: Expose PEBS feature to guest Luwei Kang
2020-03-05 17:57 ` [PATCH v1 10/11] KVM: x86/pmu: Introduce the mask value for fixed counter Luwei Kang
2020-03-05 17:57 ` [PATCH v1 11/11] KVM: x86/pmu: Adaptive PEBS virtualization enabling Luwei Kang
2020-03-05 22:48 ` [PATCH v1 00/11] PEBS virtualization enabling via DS Andi Kleen
2020-03-06 5:37 ` Kang, Luwei
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