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cpufreq: pcc: Fix the potentinal scheduling delays in target_index()

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pcc_cpufreq_target():
	cpufreq_freq_transition_begin();
	spin_lock(&pcc_lock);
	[critical section]
	cpufreq_freq_transition_end();
	spin_unlock(&pcc_lock);

Above code has a performance issue, consider that Task0 executes
'cpufreq_freq_transition_end()' to wake Task1 and preempted imediatedly
without releasing 'pcc_lock', then Task1 needs to wait for Task0 to
release 'pcc_lock'. In the worst case, this locking order can result in
Task1 wasting two scheduling rounds before it can enter the critical
section.

Signed-off-by: Liao Chang <liaochang1@huawei.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Liao Chang 2023-08-26 09:57:43 +00:00 committed by Rafael J. Wysocki
parent 916f138840
commit 4c2fdf7393
1 changed files with 1 additions and 1 deletions
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2
drivers/cpufreq/pcc-cpufreq.c
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@ -232,8 +232,8 @@ static int pcc_cpufreq_target(struct cpufreq_policy *policy,
status = ioread16(&pcch_hdr->status);
iowrite16(0, &pcch_hdr->status);
cpufreq_freq_transition_end(policy, &freqs, status != CMD_COMPLETE);
spin_unlock(&pcc_lock);
cpufreq_freq_transition_end(policy, &freqs, status != CMD_COMPLETE);
if (status != CMD_COMPLETE) {
pr_debug("target: FAILED for cpu %d, with status: 0x%x\n",