linux-kernel - Re: [RFT][PATCH v1 8/8] cpufreq: intel_pstate: EAS: Increase cost for CPUs using L3 cache

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1c6b70d1-279c-4d9d-ae31-2751daed04f6@arm.com>
Date: Fri, 25 Apr 2025 22:32:17 +0100
From: Christian Loehle <christian.loehle@....com>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>,
 Linux PM <linux-pm@...r.kernel.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Lukasz Luba <lukasz.luba@....com>,
 Peter Zijlstra <peterz@...radead.org>,
 Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
 Dietmar Eggemann <dietmar.eggemann@....com>,
 Morten Rasmussen <morten.rasmussen@....com>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
 Pierre Gondois <pierre.gondois@....com>
Subject: Re: [RFT][PATCH v1 8/8] cpufreq: intel_pstate: EAS: Increase cost for
 CPUs using L3 cache

On 4/16/25 19:12, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> On some hybrid platforms some efficient CPUs (E-cores) are not connected
> to the L3 cache, but there are no other differences between them and the
> other E-cores that use L3.  In that case, it is generally more efficient
> to run "light" workloads on the E-cores that do not use L3 and allow all
> of the cores using L3, including P-cores, to go into idle states.
> 
> For this reason, slightly increase the cost for all CPUs sharing the L3
> cache to make EAS prefer CPUs that do not use it to the other CPUs with
> the same perf-to-frequency scaling factor (if any).
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
>  drivers/cpufreq/intel_pstate.c |    8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> --- a/drivers/cpufreq/intel_pstate.c
> +++ b/drivers/cpufreq/intel_pstate.c
> @@ -979,6 +979,7 @@
>  			   unsigned long *cost)
>  {
>  	struct pstate_data *pstate = &all_cpu_data[dev->id]->pstate;
> +	struct cpu_cacheinfo *cacheinfo = get_cpu_cacheinfo(dev->id);
>  
>  	/*
>  	 * The smaller the perf-to-frequency scaling factor, the larger the IPC
> @@ -991,6 +992,13 @@
>  	 * of the same type in different "utilization bins" is different.
>  	 */
>  	*cost = div_u64(100ULL * INTEL_PSTATE_CORE_SCALING, pstate->scaling) + freq;
> +	/*
> +	 * Inrease the cost slightly for CPUs able to access L3 to avoid litting

s/Inrease/Increase
and I guess s/litting/littering

> +	 * it up too eagerly in case some other CPUs of the same type cannot
> +	 * access it.
> +	 */
> +	if (cacheinfo->num_levels >= 3)
> +		(*cost)++;

This makes cost(OPP1) of the SoC Tile e-core as expensive as cost(OPP0) of a
normal e-core.
Is that the intended behaviour?