Re: [v3, 3/3] MIPS: VDSO: Add implementations of gettimeofday() and clock_gettime()

[Leonid Yegoshin]

On 10/28/2015 12:55 PM, Alex Smith wrote:
> On 28 October 2015 at 19:28, Leonid Yegoshin <Leonid.Yegoshin@xxxxxxxxxx> wrote:
> > . 
> Clocksources are not per-CPU. If the CP0 counter is the current
> clocksource, then both the kernel and VDSO implementations of
> gettimeofday will read out the CP0 counter from whatever CPU they run
> on.

OK, it was an invalid example. Let's be specific - in case of different 
clock frequency in different CPUs it easy to adjust it in kernel via 
clocksource->read()/etc but it is impossible to adjust that in VDSO 
implementation.

And that can't be fixed easily without some-kind of "per-thread" data 
page for correct multipliers.

There are many problems with assumption that in all kind of MIPS cores 
R4K CP0_COUNT registers are in sync in different CPUs. Even current 
kernel has problems here but I think it is not excuse to mount more on it.

- Leonid.


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