Re: [PATCH v2 2/2] powercap/rapl: reduce ipi calls

Srinivas Pandruvada
2016-01-13T21:56:06Z

On Wed, 2016-01-13 at 22:26 +0100, Borislav Petkov wrote:

[Cut]

>
> rmwmsrl_safe_on_cpu(policy->cpu, MSR_IA32_PERF_CTL,
>     INTEL_PERF_CTL_MASK,
>     (u32)sfi_cpufreq_array[next_perf_state].ctr
> l_val & INTEL_PERF_CTL_MASK);
>
> Yikes!
>
> So yes, it can work but it is ugly, hard to parse and use, not
> generic
> enough, etc, etc.
>
> So thanks, but no thanks.
>
I agree, in some cases it will not make much sense to use read-
modify_write calls, the user may decide whether it makes sense or not.
But such interface is not new to Linux kernel:

regmap_update_bits(), which is referenced for 346 times.

Are you saying that any such calls are not useful?

Thanks,
Srinivas