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From: Juergen Gross via Virtualization <virtualization@lists.linux-foundation.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: kvm@vger.kernel.org,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	virtualization@lists.linux-foundation.org,
	H Peter Anvin <hpa@zytor.com>, Jiri Olsa <jolsa@redhat.com>,
	sthemmin@microsoft.com, x86@kernel.org, pv-drivers@vmware.com,
	Ingo Molnar <mingo@redhat.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Andrew.Cooper3@citrix.com, Borislav Petkov <bp@alien8.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	Mathieu Poirier <mathieu.poirier@linaro.org>,
	seanjc@google.com, Adrian Hunter <adrian.hunter@intel.com>,
	linux-kernel@vger.kernel.org, Leo Yan <leo.yan@linaro.org>,
	pbonzini@redhat.com
Subject: Re: [PATCH V2 03/11] perf/x86: Add support for TSC in nanoseconds as a perf event clock
Date: Mon, 7 Mar 2022 11:58:19 +0100	[thread overview]
Message-ID: <b3d6e048-6922-ce00-7c1f-3702695c2974@suse.com> (raw)
In-Reply-To: <YiXgirw1kFOPgBgY@hirez.programming.kicks-ass.net>


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On 07.03.22 11:38, Peter Zijlstra wrote:
> On Mon, Mar 07, 2022 at 11:06:46AM +0100, Juergen Gross wrote:
> 
>>> diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
>>> index 4420499f7bb4..a1f179ed39bf 100644
>>> --- a/arch/x86/kernel/paravirt.c
>>> +++ b/arch/x86/kernel/paravirt.c
>>> @@ -145,6 +145,15 @@ DEFINE_STATIC_CALL(pv_sched_clock, native_sched_clock);
>>>    void paravirt_set_sched_clock(u64 (*func)(void))
>>>    {
>>> +	/*
>>> +	 * Anything with ART on promises to have sane TSC, otherwise the whole
>>> +	 * ART thing is useless. In order to make ART useful for guests, we
>>> +	 * should continue to use the TSC. As such, ignore any paravirt
>>> +	 * muckery.
>>> +	 */
>>> +	if (cpu_feature_enabled(X86_FEATURE_ART))
>>> +		return;
>>> +
>>>    	static_call_update(pv_sched_clock, func);
>>>    }
>>>
>>
>> NAK, this will break live migration of a guest coming from a host
>> without this feature.
> 
> I thought the whole live-migration nonsense made sure to equalize crud
> like that. That is, then don't expose ART to the guest.

Oh, right. I managed to confuse host-side and guest-side usage.

Sorry for the noise.


Juergen

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_______________________________________________
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WARNING: multiple messages have this Message-ID (diff)
From: Juergen Gross <jgross@suse.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Jiri Olsa <jolsa@redhat.com>,
	linux-kernel@vger.kernel.org,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	x86@kernel.org, kvm@vger.kernel.org,
	H Peter Anvin <hpa@zytor.com>,
	Mathieu Poirier <mathieu.poirier@linaro.org>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Leo Yan <leo.yan@linaro.org>,
	sdeep@vmware.com, pv-drivers@vmware.com, pbonzini@redhat.com,
	seanjc@google.com, kys@microsoft.com, sthemmin@microsoft.com,
	virtualization@lists.linux-foundation.org,
	Andrew.Cooper3@citrix.com
Subject: Re: [PATCH V2 03/11] perf/x86: Add support for TSC in nanoseconds as a perf event clock
Date: Mon, 7 Mar 2022 11:58:19 +0100	[thread overview]
Message-ID: <b3d6e048-6922-ce00-7c1f-3702695c2974@suse.com> (raw)
In-Reply-To: <YiXgirw1kFOPgBgY@hirez.programming.kicks-ass.net>


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On 07.03.22 11:38, Peter Zijlstra wrote:
> On Mon, Mar 07, 2022 at 11:06:46AM +0100, Juergen Gross wrote:
> 
>>> diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
>>> index 4420499f7bb4..a1f179ed39bf 100644
>>> --- a/arch/x86/kernel/paravirt.c
>>> +++ b/arch/x86/kernel/paravirt.c
>>> @@ -145,6 +145,15 @@ DEFINE_STATIC_CALL(pv_sched_clock, native_sched_clock);
>>>    void paravirt_set_sched_clock(u64 (*func)(void))
>>>    {
>>> +	/*
>>> +	 * Anything with ART on promises to have sane TSC, otherwise the whole
>>> +	 * ART thing is useless. In order to make ART useful for guests, we
>>> +	 * should continue to use the TSC. As such, ignore any paravirt
>>> +	 * muckery.
>>> +	 */
>>> +	if (cpu_feature_enabled(X86_FEATURE_ART))
>>> +		return;
>>> +
>>>    	static_call_update(pv_sched_clock, func);
>>>    }
>>>
>>
>> NAK, this will break live migration of a guest coming from a host
>> without this feature.
> 
> I thought the whole live-migration nonsense made sure to equalize crud
> like that. That is, then don't expose ART to the guest.

Oh, right. I managed to confuse host-side and guest-side usage.

Sorry for the noise.


Juergen

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  reply	other threads:[~2022-03-07 10:58 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-02-14 11:09 [PATCH V2 00/11] perf intel-pt: Add perf event clocks to better support VM tracing Adrian Hunter
2022-02-14 11:09 ` [PATCH V2 01/11] perf/x86: Fix native_perf_sched_clock_from_tsc() with __sched_clock_offset Adrian Hunter
2022-02-14 11:09 ` [PATCH V2 02/11] perf/x86: Add support for TSC as a perf event clock Adrian Hunter
2022-03-04 12:30   ` Peter Zijlstra
2022-03-04 13:03     ` Adrian Hunter
2022-03-04 12:32   ` Peter Zijlstra
2022-03-04 17:51     ` Thomas Gleixner
2022-03-04 12:33   ` Peter Zijlstra
2022-03-04 12:41     ` Adrian Hunter
2022-02-14 11:09 ` [PATCH V2 03/11] perf/x86: Add support for TSC in nanoseconds " Adrian Hunter
2022-03-04 13:41   ` Peter Zijlstra
2022-03-04 18:27     ` Adrian Hunter
2022-03-07  9:50       ` Peter Zijlstra
2022-03-07  9:50         ` Peter Zijlstra
2022-03-07 10:06         ` Juergen Gross via Virtualization
2022-03-07 10:06           ` Juergen Gross
2022-03-07 10:38           ` Peter Zijlstra
2022-03-07 10:38             ` Peter Zijlstra
2022-03-07 10:58             ` Juergen Gross via Virtualization [this message]
2022-03-07 10:58               ` Juergen Gross
2022-03-07 12:36         ` Adrian Hunter
2022-03-07 14:42           ` Peter Zijlstra
2022-03-07 14:42             ` Peter Zijlstra
2022-03-08 14:23             ` Adrian Hunter
2022-03-08 21:06               ` Hall, Christopher S
2022-03-14 11:50                 ` Adrian Hunter
2022-04-25  5:30                   ` Adrian Hunter
2022-04-25  9:32                     ` Thomas Gleixner
2022-04-25  9:32                       ` Thomas Gleixner
2022-04-25 13:15                       ` Adrian Hunter
2022-04-25 17:05                         ` Thomas Gleixner
2022-04-25 17:05                           ` Thomas Gleixner
2022-04-26  6:51                           ` Adrian Hunter
2022-04-27 23:10                             ` Thomas Gleixner
2022-04-27 23:10                               ` Thomas Gleixner
2022-05-16  7:20                               ` Adrian Hunter
2022-02-14 11:09 ` [PATCH V2 04/11] perf tools: Add new perf clock IDs Adrian Hunter
2022-02-14 11:09 ` [PATCH V2 05/11] perf tools: Add API probes for new " Adrian Hunter
2022-02-14 11:09 ` [PATCH V2 06/11] perf tools: Add new clock IDs to "perf time to TSC" test Adrian Hunter
2022-02-14 11:09 ` [PATCH V2 07/11] perf tools: Add perf_read_tsc_conv_for_clockid() Adrian Hunter
2022-02-14 11:09 ` [PATCH V2 08/11] perf intel-pt: Add support for new clock IDs Adrian Hunter
2022-02-14 11:09 ` [PATCH V2 09/11] perf intel-pt: Use CLOCK_PERF_HW_CLOCK_NS by default Adrian Hunter
2022-02-14 11:09 ` [PATCH V2 10/11] perf intel-pt: Add config variables for timing parameters Adrian Hunter
2022-02-14 11:09 ` [PATCH V2 11/11] perf intel-pt: Add documentation for new clock IDs Adrian Hunter
2022-02-21  6:54 ` [PATCH V2 00/11] perf intel-pt: Add perf event clocks to better support VM tracing Adrian Hunter
2022-03-01 11:06   ` Adrian Hunter

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