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Date:   Tue, 27 Sep 2022 14:53:29 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Cc:     Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Ricardo Neri <ricardo.neri@intel.com>,
        "Ravi V. Shankar" <ravi.v.shankar@intel.com>,
        Ben Segall <bsegall@google.com>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Len Brown <len.brown@intel.com>, Mel Gorman <mgorman@suse.de>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Valentin Schneider <vschneid@redhat.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org, "Tim C . Chen" <tim.c.chen@intel.com>
Subject: Re: [RFC PATCH 23/23] x86/process: Reset hardware history in context
 switch
Message-ID: <YzLySV4545F0MKSl@hirez.programming.kicks-ass.net>
References: <20220909231205.14009-1-ricardo.neri-calderon@linux.intel.com>
 <20220909231205.14009-24-ricardo.neri-calderon@linux.intel.com>
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In-Reply-To: <20220909231205.14009-24-ricardo.neri-calderon@linux.intel.com>
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On Fri, Sep 09, 2022 at 04:12:05PM -0700, Ricardo Neri wrote:
> Reset the classification history of the current task when switching to
> the next task. Hardware will start anew the classification of the next
> running task.

Please quantify the cost of this HRESET instruction.

> diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
> index 2f314b170c9f..74d8ad83e0b3 100644
> --- a/arch/x86/kernel/process_32.c
> +++ b/arch/x86/kernel/process_32.c
> @@ -52,6 +52,7 @@
>  #include <asm/switch_to.h>
>  #include <asm/vm86.h>
>  #include <asm/resctrl.h>
> +#include <asm/hreset.h>
>  #include <asm/proto.h>
>  
>  #include "process.h"
> @@ -214,6 +215,8 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
>  	/* Load the Intel cache allocation PQR MSR. */
>  	resctrl_sched_in();
>  
> +	reset_hardware_history();
> +
>  	return prev_p;
>  }
>  
> diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
> index 1962008fe743..0b175f30f359 100644
> --- a/arch/x86/kernel/process_64.c
> +++ b/arch/x86/kernel/process_64.c
> @@ -53,6 +53,7 @@
>  #include <asm/xen/hypervisor.h>
>  #include <asm/vdso.h>
>  #include <asm/resctrl.h>
> +#include <asm/hreset.h>
>  #include <asm/unistd.h>
>  #include <asm/fsgsbase.h>
>  #ifdef CONFIG_IA32_EMULATION
> @@ -657,6 +658,8 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
>  	/* Load the Intel cache allocation PQR MSR. */
>  	resctrl_sched_in();
>  
> +	reset_hardware_history();
> +
>  	return prev_p;
>  }
>  
> -- 
> 2.25.1
>