Re: [PATCH 11/15] x86: Rewrite cyc2ns to avoid the need to disable IRQs

[Mauro]

On 17-06-2014 13:42, Viresh Kumar wrote:
>> So what you can try is force a cyc2ns read before the write in
>> set_cyc2ns_scale(). I think its possible that if we do not do the read,
>> the write will wait for a 'free' slot indefinitely.
> 
> Hmm, I see. Thanks for your quick response.
> 
> Are you suggesting something like this ? :
> 
> diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
> index 57e5ce1..290ac03 100644
> --- a/arch/x86/kernel/tsc.c
> +++ b/arch/x86/kernel/tsc.c
> @@ -249,6 +249,9 @@ static void set_cyc2ns_scale(unsigned long cpu_khz, int cpu)
>         if (!cpu_khz)
>                 goto done;
> 
> +       data = cyc2ns_read_begin();
> +       cyc2ns_read_end(data);
> +
>         data = cyc2ns_write_begin(cpu);
> 
>         rdtscll(tsc_now);
> 
> 
> @Mauro: Please try this once Peter confirms.

I have tried this and it doesn't solve the problem, the machine still
hangs after the second frequency change after cpu offline/online.
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