commit 4e8a0bfc7bf709e753ea0ef4e653e3e39a282895
author Narayanan Gopalakrishnan <nargop@codeaurora.org> Thu Nov 01 10:08:55 2012 -0700
committer Narayanan Gopalakrishnan <nargop@codeaurora.org> Mon Nov 05 11:42:00 2012 -0800
tree 561ca1ac55d166830b033d17548171a88459b3cb
parent 27470721eda7c766786a85f0d21c69e3e333914a

msm: cpufreq: increase priority of thread that increases frequencies

When the cpufreq governors request for increase in frequency from kworker
threads, there is chance that the kworker thread is cpu starved due to
other high priority threads, leading to undesirable increase in frequency
ramp-up latency. Add the calling thread to SCHED_FIFO policy when
requesting for increase in frequency and restore back to original policy
after ramp-up is completed.

Change-Id: Ie4fa199b7f9087717cb94dfcc2eddea27cc0012b
Signed-off-by: Narayanan Gopalakrishnan <nargop@codeaurora.org>

arch/arm/mach-msm/cpufreq.c

diff --git a/arch/arm/mach-msm/cpufreq.c b/arch/arm/mach-msm/cpufreq.c
index 6c9b413..e0d98b7 100644
--- a/arch/arm/mach-msm/cpufreq.c
+++ b/arch/arm/mach-msm/cpufreq.c
@@ -52,8 +52,11 @@
 static int set_cpu_freq(struct cpufreq_policy *policy, unsigned int new_freq)
 {
 	int ret = 0;
+	int saved_sched_policy = -EINVAL;
+	int saved_sched_rt_prio = -EINVAL;
 	struct cpufreq_freqs freqs;
 	struct cpu_freq *limit = &per_cpu(cpu_freq_info, policy->cpu);
+	struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
 
 	if (limit->limits_init) {
 		if (new_freq > limit->allowed_max) {
@@ -70,11 +73,29 @@
 	freqs.old = policy->cur;
 	freqs.new = new_freq;
 	freqs.cpu = policy->cpu;
+
+	/*
+	 * Put the caller into SCHED_FIFO priority to avoid cpu starvation
+	 * in the acpuclk_set_rate path while increasing frequencies
+	 */
+
+	if (freqs.new > freqs.old && current->policy != SCHED_FIFO) {
+		saved_sched_policy = current->policy;
+		saved_sched_rt_prio = current->rt_priority;
+		sched_setscheduler_nocheck(current, SCHED_FIFO, &param);
+	}
+
 	cpufreq_notify_transition(&freqs, CPUFREQ_PRECHANGE);
+
 	ret = acpuclk_set_rate(policy->cpu, new_freq, SETRATE_CPUFREQ);
 	if (!ret)
 		cpufreq_notify_transition(&freqs, CPUFREQ_POSTCHANGE);
 
+	/* Restore priority after clock ramp-up */
+	if (freqs.new > freqs.old && saved_sched_policy >= 0) {
+		param.sched_priority = saved_sched_rt_prio;
+		sched_setscheduler_nocheck(current, saved_sched_policy, &param);
+	}
 	return ret;
 }