Re: [PATCH v12 03/11] x86/tsc: redefine notsc to behave as tsc=unstable

[Thomas Gleixner]

On Thu, 21 Jun 2018, Pavel Tatashin wrote:
> Currently, notsc kernel parameter disables the use of tsc register by
> sched_clock(). However, this parameter does not prevent linux from
> accessing tsc in other places in kernel.
> 
> The only rational to boot with notsc is to avoid timing discrepancies on
> multi-socket systems where different tsc frequencies may present, and thus
> fallback to jiffies for clock source.
> 
> However, there is another method to solve the above problem, it is to boot
> with tsc=unstable parameter. This parameter allows sched_clock() to use tsc
> but in case tsc is outside of expected interval it is corrected back to a
> sane value.
> 
> This is why there is no reason to keep notsc, and it can be removed. But,
> for compatibility reasons we will keep this parameter but change its
> definition to be the same as tsc=unstable.
> 
> Signed-off-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
> Reviewed-by: Dou Liyang <douly.fnst@xxxxxxxxxxxxxx>

Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>