From a59d1637eb0e0a37ee0e5c92800c60abe3624e24 Mon Sep 17 00:00:00 2001 From: "Pallipadi, Venkatesh" Date: Thu, 19 Mar 2009 14:41:40 -0700 Subject: ACPI: cap off P-state transition latency from buggy BIOSes Some BIOSes report very high frequency transition latency which are plainly wrong on CPus that can change frequency using native MSR interface. One such system is IBM T42 (2327-8ZU) as reported by Owen Taylor and Rik van Riel. cpufreq_ondemand driver uses this transition latency to come up with a reasonable sampling interval to sample CPU usage and with such high latency value, ondemand sampling interval ends up being very high (0.5 sec, in this particular case), resulting in performance impact due to slow response to increasing frequency. Fix it by capping-off the transition latency to 20uS for native MSR based frequency transitions. mjg: We've confirmed that this also helps on the X31 Signed-off-by: Venkatesh Pallipadi Acked-by: Matthew Garrett Signed-off-by: Len Brown --- arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) (limited to 'arch') diff --git a/arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c b/arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c index 4b1c319d30c..89c676d6caf 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; istate_count; i++) { -- cgit v1.2.3 From 5b4c0b6fffb91b07a6f85dabbdfbd5abab61d9db Mon Sep 17 00:00:00 2001 From: Zhang Rui Date: Wed, 1 Apr 2009 01:49:42 -0400 Subject: ACPI: update comment update ACPI Development Discussion List Signed-off-by: Zhang Rui Signed-off-by: Len Brown --- arch/x86/kernel/acpi/boot.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'arch') diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c index 7678f10c456..2481ec3e83b 100644 --- a/arch/x86/kernel/acpi/boot.c +++ b/arch/x86/kernel/acpi/boot.c @@ -1493,7 +1493,7 @@ static int __init dmi_ignore_irq0_timer_override(const struct dmi_system_id *d) /* * If your system is blacklisted here, but you find that acpi=force - * works for you, please contact acpi-devel@sourceforge.net + * works for you, please contact linux-acpi@vger.kernel.org */ static struct dmi_system_id __initdata acpi_dmi_table[] = { /* -- cgit v1.2.3