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From: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
To: Dave Hansen <dave.hansen@intel.com>
Cc: linux-kernel@vger.kernel.org, linux-tip-commits@vger.kernel.org,
	"Peter Zijlstra (Intel)" <peterz@infradead.org>,
	Tony Luck <tony.luck@intel.com>, Len Brown <len.brown@intel.com>,
	Borislav Petkov <bp@suse.de>,
	x86@kernel.org
Subject: Re: [tip: perf/core] x86/cpu: Add helper function to get the type of the current hybrid CPU
Date: Wed, 10 May 2023 16:56:35 -0700	[thread overview]
Message-ID: <20230510235635.GC18514@ranerica-svr.sc.intel.com> (raw)
In-Reply-To: <25fe5313-97de-1528-e13e-f3b6286a8385@intel.com>

On Wed, May 10, 2023 at 11:33:40AM -0700, Dave Hansen wrote:
> On 5/10/23 11:18, Ricardo Neri wrote:
> >> Sorry to dredge up an old thread.  But, where does this information
> >> about "If the processor is not hybrid, returns 0." come from?
> >>
> >> What is there to keep cpuid_eax(0x0000001a) from having 0x0 in those
> >> bits?  Seems to me like 0 is theoretically a valid hybrid CPU type.  Right?
> > My reasoning was that according to the Intel SDM the only valid values were
> > 0x20 and 0x40. 0 was meant to be an invalid value.
> 
> That doesn't make any sense to me really.  Just because today's SDM
> doesn't have a value doesn't mean that it becomes an invalid value tomorrow.
> 
> For instance, there's no model 0xEE today.  But that doesn't make it
> *INVALID*, it just means there's not one defined *today*.  Today's
> kernel shouldn't fall over if it runs on an model==0xEE system.

Yes, I agree. 0 may become a valid value tomorrow.

> 
> > I read the SDM again. It seems that cpuid_eax(0x0000001a) already returns
> > 0 when the leaf does not exist.
> 
> Right, but this isn't really relevant here either.  A CPU's APICID comes
> out of a leaf that can be unsupported (not exist).  That doesn't make
> APICID==0 invalid in any way.

But you always need an APICID, no? You would only need to get the CPU type
only when running on a hybrid CPU; from cpuid_eax(0x0000001a) or any other
future mechanism. Yes, I agree that is plausible to have 0 as the CPU type.

> 
> > Probably the check for X86_FEATURE_HYBRID_CPU is not needed.
> > 
> > Still, callers need to check for a valid value, IMO.
> 
> Right.  But if they're just going to check the number that comes back
> from this function, 0 can't represent an invalid value.

So maybe changing the function to return -ENOTSUP or -ENODEV on a non-hybrid
processor?

  parent reply	other threads:[~2023-05-10 23:53 UTC|newest]

Thread overview: 56+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-12 14:30 [PATCH V6 00/25] Add Alder Lake support for perf (kernel) kan.liang
2021-04-12 14:30 ` [PATCH V6 01/25] x86/cpufeatures: Enumerate Intel Hybrid Technology feature bit kan.liang
2021-04-20 10:46   ` [tip: perf/core] " tip-bot2 for Ricardo Neri
2021-04-12 14:30 ` [PATCH V6 02/25] x86/cpu: Add helper function to get the type of the current hybrid CPU kan.liang
2021-04-20 10:46   ` [tip: perf/core] " tip-bot2 for Ricardo Neri
2023-05-05 16:42     ` Dave Hansen
2023-05-10 18:18       ` Ricardo Neri
2023-05-10 18:33         ` Dave Hansen
2023-05-10 19:15           ` Luck, Tony
2023-05-10 23:56           ` Ricardo Neri [this message]
2021-04-12 14:30 ` [PATCH V6 03/25] perf/x86: Track pmu in per-CPU cpu_hw_events kan.liang
2021-04-20 10:46   ` [tip: perf/core] " tip-bot2 for Kan Liang
2021-04-12 14:30 ` [PATCH V6 04/25] perf/x86/intel: Hybrid PMU support for perf capabilities kan.liang
2021-04-20 10:46   ` [tip: perf/core] " tip-bot2 for Kan Liang
2021-04-12 14:30 ` [PATCH V6 05/25] perf/x86: Hybrid PMU support for intel_ctrl kan.liang
2021-04-20 10:46   ` [tip: perf/core] " tip-bot2 for Kan Liang
2021-04-12 14:30 ` [PATCH V6 06/25] perf/x86: Hybrid PMU support for counters kan.liang
2021-04-20 10:46   ` [tip: perf/core] " tip-bot2 for Kan Liang
2021-04-12 14:30 ` [PATCH V6 07/25] perf/x86: Hybrid PMU support for unconstrained kan.liang
2021-04-20 10:46   ` [tip: perf/core] " tip-bot2 for Kan Liang
2021-04-12 14:30 ` [PATCH V6 08/25] perf/x86: Hybrid PMU support for hardware cache event kan.liang
2021-04-20 10:46   ` [tip: perf/core] " tip-bot2 for Kan Liang
2021-04-12 14:30 ` [PATCH V6 09/25] perf/x86: Hybrid PMU support for event constraints kan.liang
2021-04-20 10:46   ` [tip: perf/core] " tip-bot2 for Kan Liang
2021-04-12 14:30 ` [PATCH V6 10/25] perf/x86: Hybrid PMU support for extra_regs kan.liang
2021-04-20 10:46   ` [tip: perf/core] " tip-bot2 for Kan Liang
2021-04-12 14:30 ` [PATCH V6 11/25] perf/x86/intel: Factor out intel_pmu_check_num_counters kan.liang
2021-04-20 10:46   ` [tip: perf/core] " tip-bot2 for Kan Liang
2021-04-12 14:30 ` [PATCH V6 12/25] perf/x86/intel: Factor out intel_pmu_check_event_constraints kan.liang
2021-04-20 10:46   ` [tip: perf/core] " tip-bot2 for Kan Liang
2021-04-12 14:30 ` [PATCH V6 13/25] perf/x86/intel: Factor out intel_pmu_check_extra_regs kan.liang
2021-04-20 10:46   ` [tip: perf/core] " tip-bot2 for Kan Liang
2021-04-12 14:30 ` [PATCH V6 14/25] perf/x86: Remove temporary pmu assignment in event_init kan.liang
2021-04-20 10:46   ` [tip: perf/core] " tip-bot2 for Kan Liang
2021-04-12 14:30 ` [PATCH V6 15/25] perf/x86: Factor out x86_pmu_show_pmu_cap kan.liang
2021-04-20 10:46   ` [tip: perf/core] " tip-bot2 for Kan Liang
2021-04-12 14:30 ` [PATCH V6 16/25] perf/x86: Register hybrid PMUs kan.liang
2021-04-20 10:46   ` [tip: perf/core] " tip-bot2 for Kan Liang
2021-04-12 14:30 ` [PATCH V6 17/25] perf/x86: Add structures for the attributes of Hybrid PMUs kan.liang
2021-04-20 10:46   ` [tip: perf/core] " tip-bot2 for Kan Liang
2021-04-12 14:30 ` [PATCH V6 18/25] perf/x86/intel: Add attr_update for " kan.liang
2021-04-20 10:46   ` [tip: perf/core] " tip-bot2 for Kan Liang
2021-04-12 14:30 ` [PATCH V6 19/25] perf/x86: Support filter_match callback kan.liang
2021-04-20 10:46   ` [tip: perf/core] " tip-bot2 for Kan Liang
2021-04-12 14:31 ` [PATCH V6 20/25] perf/x86/intel: Add Alder Lake Hybrid support kan.liang
2021-04-20 10:46   ` [tip: perf/core] " tip-bot2 for Kan Liang
2021-04-12 14:31 ` [PATCH V6 21/25] perf: Extend PERF_TYPE_HARDWARE and PERF_TYPE_HW_CACHE kan.liang
2021-04-20 10:46   ` [tip: perf/core] " tip-bot2 for Kan Liang
2021-04-12 14:31 ` [PATCH V6 22/25] perf/x86/intel/uncore: Add Alder Lake support kan.liang
2021-04-20 10:46   ` [tip: perf/core] " tip-bot2 for Kan Liang
2021-04-12 14:31 ` [PATCH V6 23/25] perf/x86/msr: Add Alder Lake CPU support kan.liang
2021-04-20 10:46   ` [tip: perf/core] " tip-bot2 for Kan Liang
2021-04-12 14:31 ` [PATCH V6 24/25] perf/x86/cstate: " kan.liang
2021-04-20 10:46   ` [tip: perf/core] " tip-bot2 for Kan Liang
2021-04-12 14:31 ` [PATCH V6 25/25] perf/x86/rapl: Add support for Intel Alder Lake kan.liang
2021-04-20 10:46   ` [tip: perf/core] " tip-bot2 for Zhang Rui

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