linux-kernel - Re: [PATCH v7 1/6] x86/tsc: remove tsc

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Message-ID: <f3bb2e30-1209-ac23-b007-d59c23a5bd24@cn.fujitsu.com>
Date:   Fri, 3 Nov 2017 09:58:51 +0800
From:   Dou Liyang <douly.fnst@...fujitsu.com>
To:     Pavel Tatashin <pasha.tatashin@...cle.com>,
        <steven.sistare@...cle.com>, <daniel.m.jordan@...cle.com>,
        <linux@...linux.org.uk>, <schwidefsky@...ibm.com>,
        <heiko.carstens@...ibm.com>, <john.stultz@...aro.org>,
        <sboyd@...eaurora.org>, <x86@...nel.org>,
        <linux-kernel@...r.kernel.org>, <mingo@...hat.com>,
        <tglx@...utronix.de>, <hpa@...or.com>
Subject: Re: [PATCH v7 1/6] x86/tsc: remove tsc_disabled flag

Hi Pavel,

At 11/03/2017 01:26 AM, Pavel Tatashin wrote:
> tsc_disabled is set when notsc is passed as kernel parameter. The reason we
> have notsc is to avoid timing problems on multi-preccors systems. However,
> we already have a mechanism to detect and resolve these issues by invoking
> tsc unstable path.
>
> Signed-off-by: Pavel Tatashin <pasha.tatashin@...cle.com>
> ---
>  arch/x86/kernel/tsc.c | 17 +++--------------
>  1 file changed, 3 insertions(+), 14 deletions(-)
>
> diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
> index 796d96bb0821..1c4502a2b7b2 100644
> --- a/arch/x86/kernel/tsc.c
> +++ b/arch/x86/kernel/tsc.c
> @@ -37,11 +37,6 @@ EXPORT_SYMBOL(tsc_khz);
>   */
>  static int __read_mostly tsc_unstable;
>
> -/* native_sched_clock() is called before tsc_init(), so
> -   we must start with the TSC soft disabled to prevent
> -   erroneous rdtsc usage on !boot_cpu_has(X86_FEATURE_TSC) processors */
> -static int __read_mostly tsc_disabled = -1;
> -
>  static DEFINE_STATIC_KEY_FALSE(__use_tsc);
>
>  int tsc_clocksource_reliable;
> @@ -248,7 +243,7 @@ EXPORT_SYMBOL_GPL(check_tsc_unstable);
>  int __init notsc_setup(char *str)
>  {
>  	pr_warn("Kernel compiled with CONFIG_X86_TSC, cannot disable TSC completely\n");

IMO, this warning may make users confused, could we remove it from here?

Thanks,
	dou.