linux-kernel - Re: [PATCH] perf/x86/amd/uncore: Use Node ID to identify DF and UMC domains

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Message-ID: <2026012245-endless-botanist-207d@gregkh>
Date: Thu, 22 Jan 2026 07:48:53 +0100
From: Greg KH <gregkh@...uxfoundation.org>
To: Sandipan Das <sandipan.das@....com>
Cc: linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	James Clark <james.clark@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H . Peter Anvin" <hpa@...or.com>, stable@...r.kernel.org,
	Ravi Bangoria <ravi.bangoria@....com>,
	Ananth Narayan <ananth.narayan@....com>
Subject: Re: [PATCH] perf/x86/amd/uncore: Use Node ID to identify DF and UMC
 domains

On Thu, Jan 22, 2026 at 12:15:05PM +0530, Sandipan Das wrote:
> For DF and UMC PMUs, a single context is shared across all CPUs that are
> connected to the same Data Fabric (DF) instance. Currently, Socket ID is
> used to identify DF instances. This approach works for configurations
> having a single IO Die (IOD) but fails in the following cases.
>   * Older Zen 1 processors, where each chiplet has its own DF instance
>     instead of a single IOD.
>   * Any configurations with multiple IODs in a single socket.
> 
> Address this by using the Node ID available in ECX[7:0] of CPUID leaf
> 0x8000001e which is already provided by topology_amd_node_id(). Replace
> the use of topology_logical_package_id() with topology_amd_node_id() in
> order to correctly identify domains for context sharing.
> 
> Fixes: 07888daa056e ("perf/x86/amd/uncore: Move discovery and registration")
> Signed-off-by: Sandipan Das <sandipan.das@....com>
> ---
>  arch/x86/events/amd/uncore.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/events/amd/uncore.c b/arch/x86/events/amd/uncore.c
> index 9293ce50574d..9a13a9f21d2f 100644
> --- a/arch/x86/events/amd/uncore.c
> +++ b/arch/x86/events/amd/uncore.c
> @@ -700,7 +700,7 @@ void amd_uncore_df_ctx_scan(struct amd_uncore *uncore, unsigned int cpu)
>  	info.split.aux_data = 0;
>  	info.split.num_pmcs = NUM_COUNTERS_NB;
>  	info.split.gid = 0;
> -	info.split.cid = topology_logical_package_id(cpu);
> +	info.split.cid = topology_amd_node_id(cpu);
>  
>  	if (pmu_version >= 2) {
>  		ebx.full = cpuid_ebx(EXT_PERFMON_DEBUG_FEATURES);
> @@ -999,8 +999,8 @@ void amd_uncore_umc_ctx_scan(struct amd_uncore *uncore, unsigned int cpu)
>  	cpuid(EXT_PERFMON_DEBUG_FEATURES, &eax, &ebx.full, &ecx, &edx);
>  	info.split.aux_data = ecx;	/* stash active mask */
>  	info.split.num_pmcs = ebx.split.num_umc_pmc;
> -	info.split.gid = topology_logical_package_id(cpu);
> -	info.split.cid = topology_logical_package_id(cpu);
> +	info.split.gid = topology_amd_node_id(cpu);
> +	info.split.cid = topology_amd_node_id(cpu);
>  	*per_cpu_ptr(uncore->info, cpu) = info;
>  }
>  
> -- 
> 2.43.0
> 
> 

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>