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

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Date:	Wed, 13 Jan 2016 10:21:38 -0800
From:	Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux PM <linux-pm@...r.kernel.org>,
	Rafael Wysocki <rafael.j.wysocki@...el.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	X86 Kernel <x86@...nel.org>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH v2 2/2] powercap/rapl: reduce ipi calls

On Wed, 13 Jan 2016 19:04:12 +0100
Borislav Petkov <bp@...en8.de> wrote:

> > Then i was suggested to add a rmw msr api for the common good :), I
> > think it is a good idea since such operation is not limited to RAPL
> > driver.  
> 
> Others are...?

nothing for the _safe version right now. Quick scan through the code
I see the non safe version has a couple can be converted to rmw.
e.g.

static int cpufreq_p4_setdc(unsigned int cpu, unsigned int newstate)
{
...

	rdmsr_on_cpu(cpu, MSR_IA32_THERM_CONTROL, &l, &h);
	if (newstate == DC_DISABLE) {
		pr_debug("CPU#%d disabling modulation\n", cpu);
		wrmsr_on_cpu(cpu, MSR_IA32_THERM_CONTROL, l & ~(1<<4),
	h); } else {
		pr_debug("CPU#%d setting duty cycle to %d%%\n",
			cpu, ((125 * newstate) / 10));
		/* bits 63 - 5	: reserved
		 * bit  4	: enable/disable
		 * bits 3-1	: duty cycle
		 * bit  0	: reserved
		 */
		l = (l & ~14);
		l = l | (1<<4) | ((newstate & 0x7)<<1);
		wrmsr_on_cpu(cpu, MSR_IA32_THERM_CONTROL, l, h);
	} 


static int sfi_cpufreq_target(struct cpufreq_policy *policy, unsigned
int index) {
...

	rdmsr_on_cpu(policy->cpu, MSR_IA32_PERF_CTL, &lo, &hi);
	lo = (lo & ~INTEL_PERF_CTL_MASK) |
		((u32) sfi_cpufreq_array[next_perf_state].ctrl_val &
		INTEL_PERF_CTL_MASK);
	wrmsr_on_cpu(policy->cpu, MSR_IA32_PERF_CTL, lo, hi);