Messages in this thread Patch in this message | | | Subject | Performance regression in 2.6.30-rc1 | From | poornima nayak <> | Date | Tue, 02 Jun 2009 16:30:19 +0530 |
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Hi
By executing kernbench on 2.6.30-rc1 we observed there is a performance regression in 2.6.30-rc1. Then git-bisect was done between v2.6.29 and v2.6.30-rc5, after 13 iterations identified the attached patch is causing regression.
Performance data of 2.6.29 without applying the attached patch. param-version testname elapsed-avg elapsed-std 2.6.29' pm_kernbench.Version-none-threads=2-sched_mc=2 221.1 0.81 2.6.29' pm_kernbench.Version-none-threads=4-sched_mc=0 115.09 0.6 2.6.29' pm_kernbench.Version-none-threads=4-sched_mc=2 109.05 0.25 2.6.29' pm_kernbench.Version-none-threads=8-sched_mc=2 60.4 0.38 2.6.29' pm_kernbench.Version-none-threads=8-sched_mc=0 65.23 0.34 2.6.29' pm_kernbench.Version-none-threads=2-sched_mc=0 231.61 0.59
Performance data of 2.6.29 after applying the attached patch. param-version testname elapsed-avg elapsed-std 2.6.29' pm_kernbench.Version-thir-bisect-threads=2-sched_mc=0 203.77 0.48 2.6.29' pm_kernbench.Version-thir-bisect-threads=8-sched_mc=0 64.38 0.25 2.6.29' pm_kernbench.Version-thir-bisect-threads=4-sched_mc=0 102.46 0.1 2.6.29' pm_kernbench.Version-thir-bisect-threads=8-sched_mc=2 59.94 0.46 2.6.29' pm_kernbench.Version-thir-bisect-threads=4-sched_mc=2 106.84 0.28 2.6.29' pm_kernbench.Version-thir-bisect-threads=2-sched_mc=2 199.44 0.44
Performance issue here is when sched_mc_power_savings is set 2 and kernbench is triggered with 4 threads the value of 'elapsed time' is more then sched_mc_power_savings is set to 0. Expectation is elapsed time should be less when sched_mc_power_savings set 2 compared to sched_mc_power_savings set to 0.
Regds Poornima diff --git a/arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c b/arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c index 4b1c319..89c676d 100644 --- a/arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c +++ b/arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c @@ -680,6 +680,18 @@ static int acpi_cpufreq_cpu_init(struct cpufreq_policy *policy) perf->states[i].transition_latency * 1000; } + /* Check for high latency (>20uS) from buggy BIOSes, like on T42 */ + if (perf->control_register.space_id == ACPI_ADR_SPACE_FIXED_HARDWARE && + policy->cpuinfo.transition_latency > 20 * 1000) { + static int print_once; + policy->cpuinfo.transition_latency = 20 * 1000; + if (!print_once) { + print_once = 1; + printk(KERN_INFO "Capping off P-state tranision latency" + " at 20 uS\n"); + } + } + data->max_freq = perf->states[0].core_frequency * 1000; /* table init */ for (i=0; i<perf->state_count; i++) { | |