linux-kernel - Re: [PATCH] x86/tsc: Use rdtsc_ordered() when RDTSCP or LFENCE

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Message-ID: <80132627-5585-456b-a8b3-788d83808d3b@kernel.org>
Date: Thu, 22 Aug 2024 23:29:33 -0500
From: Mario Limonciello <superm1@...nel.org>
To: Bjorn Helgaas <bhelgaas@...gle.com>,
 Mathias Nyman <mathias.nyman@...el.com>,
 Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc: "open list : PCI SUBSYSTEM" <linux-pci@...r.kernel.org>,
 open list <linux-kernel@...r.kernel.org>,
 "open list : USB XHCI DRIVER" <linux-usb@...r.kernel.org>,
 Daniel Drake <drake@...lessos.org>, Gary Li <Gary.Li@....com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
 Mario Limonciello <mario.limonciello@....com>
Subject: Re: [PATCH] x86/tsc: Use rdtsc_ordered() when RDTSCP or LFENCE_RDTSC
 are supported



On 8/22/24 23:25, Mario Limonciello wrote:
> From: Mario Limonciello <mario.limonciello@....com>
> 
> On AMD processors the TSC has been reported drifting on and off for
> various platforms.  This has been root caused to becaused by out of order
> TSC and HPET counter values.  When the SoC supports RDTSCP or LFENCE_RDTSC
> use ordered tsc reads instead.
> 
> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
> ---
>   arch/x86/include/asm/tsc.h | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/arch/x86/include/asm/tsc.h b/arch/x86/include/asm/tsc.h
> index 94408a784c8e7..1c0cda1702bec 100644
> --- a/arch/x86/include/asm/tsc.h
> +++ b/arch/x86/include/asm/tsc.h
> @@ -24,6 +24,9 @@ static inline cycles_t get_cycles(void)
>   	if (!IS_ENABLED(CONFIG_X86_TSC) &&
>   	    !cpu_feature_enabled(X86_FEATURE_TSC))
>   		return 0;
> +	if (cpu_feature_enabled(X86_FEATURE_LFENCE_RDTSC) ||
> +	    cpu_feature_enabled(X86_FEATURE_RDTSCP))
> +		return rdtsc_ordered();
>   	return rdtsc();
>   }
>   #define get_cycles get_cycles

Sorry; this unrelated patch I didn't intend to include in the series, it 
was in my working directory by accident.  Please disregard it for now, 
but review the rest of the series.

Thanks!