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SubjectRe: [linux-pm] [PATCH] cpuidle: avoid singing capacitors
On Thu, 13 Mar 2008 17:34:37 +0100
Pierre Ossman <drzeus-list@drzeus.cx> wrote:

> On Wed, 12 Mar 2008 15:11:17 -0400
> Len Brown <lenb@kernel.org> wrote:
>
> >
> > You'll see "desc" change if ACPI pulls a _CST change on you.
> >
>
> It does not. But my C3 desc looks like this:
>
> state3/desc:ACPI FFH INTEL MWAIT 0x50
>

I must have done something wrong. I now see a switch between C6 and C3
when I play with the AC cord.

On that theme, I've tested fiddling with the real C-states. I've added
a new max_hwcstate that makes ACPI downgrade MWAIT hints. I also made
some odd discoveries:

C3: More or less completely silent (I haven't tested it in a really
quiet environment yet).
C4: Constant noise
C5: Constant noise
C6: Intermittent noise

When I say constant, I mean that the noise is not generated as a result
of switching between modes (to any extent I can see at least). The
average time spent in C3 (as reported by Powertop) is over 200 ms. So
that would give a frequency of around 5 Hz, not a consistent tone of
several kHz.

Here's said patch. Please comment as I hope this can be merged:

diff --git a/arch/x86/kernel/acpi/cstate.c b/arch/x86/kernel/acpi/cstate.c
index 8ca3557..389ea8b 100644
--- a/arch/x86/kernel/acpi/cstate.c
+++ b/arch/x86/kernel/acpi/cstate.c
@@ -47,6 +47,9 @@ EXPORT_SYMBOL(acpi_processor_power_init_bm_check);

/* The code below handles cstate entry with monitor-mwait pair on Intel*/

+static unsigned int max_hwcstate __read_mostly = -1;
+module_param(max_hwcstate, uint, 0644);
+
struct cstate_entry {
struct {
unsigned int eax;
@@ -80,6 +83,7 @@ int acpi_processor_ffh_cstate_probe(unsigned int cpu,
unsigned int edx_part;
unsigned int cstate_type; /* C-state type and not ACPI C-state type */
unsigned int num_cstate_subtype;
+ unsigned int hint;

if (!cpu_cstate_entry || c->cpuid_level < CPUID_MWAIT_LEAF )
return -1;
@@ -100,16 +104,40 @@ int acpi_processor_ffh_cstate_probe(unsigned int cpu,
cpuid(CPUID_MWAIT_LEAF, &eax, &ebx, &ecx, &edx);

/* Check whether this particular cx_type (in CST) is supported or not */
- cstate_type = (cx->address >> MWAIT_SUBSTATE_SIZE) + 1;
- edx_part = edx >> (cstate_type * MWAIT_SUBSTATE_SIZE);
- num_cstate_subtype = edx_part & MWAIT_SUBSTATE_MASK;
+ hint = cx->address;
+ for (;;) {
+ /* Compute main C-state */
+ cstate_type = (hint >> MWAIT_SUBSTATE_SIZE) + 1;
+
+ /* Determine number of sub-states for this C-state */
+ edx_part = edx >> (cstate_type * MWAIT_SUBSTATE_SIZE);
+ num_cstate_subtype = edx_part & MWAIT_SUBSTATE_MASK;
+
+ /* Check if it's within constraints, and supported */
+ if ((cstate_type > max_hwcstate) ||
+ (num_cstate_subtype <=
+ (hint & MWAIT_SUBSTATE_MASK))) {
+ /* Move down a C-state and drop sub-state */
+ cstate_type--;
+ hint = (cstate_type - 1) << MWAIT_SUBSTATE_SIZE;
+ /* Out of states, abort */
+ if (cstate_type == 0) {
+ retval = -1;
+ goto out;
+ }
+ } else {
+ break;
+ }
+ }

- retval = 0;
- if (num_cstate_subtype < (cx->address & MWAIT_SUBSTATE_MASK)) {
- retval = -1;
- goto out;
+ if (hint != cx->address) {
+ printk(KERN_DEBUG "ACPI: Downgrading hardware C%d to C%d\n",
+ (cx->address >> MWAIT_SUBSTATE_SIZE) + 1,
+ (hint >> MWAIT_SUBSTATE_SIZE) + 1);
}

+ retval = 0;
+
/* mwait ecx extensions INTERRUPT_BREAK should be supported for C2/C3 */
if (!(ecx & CPUID5_ECX_EXTENSIONS_SUPPORTED) ||
!(ecx & CPUID5_ECX_INTERRUPT_BREAK)) {
@@ -119,15 +147,15 @@ int acpi_processor_ffh_cstate_probe(unsigned int cpu,
percpu_entry->states[cx->index].ecx = MWAIT_ECX_INTERRUPT_BREAK;

/* Use the hint in CST */
- percpu_entry->states[cx->index].eax = cx->address;
+ percpu_entry->states[cx->index].eax = hint;

if (!mwait_supported[cstate_type]) {
mwait_supported[cstate_type] = 1;
printk(KERN_DEBUG "Monitor-Mwait will be used to enter C-%d "
"state\n", cx->type);
}
- snprintf(cx->desc, ACPI_CX_DESC_LEN, "ACPI FFH INTEL MWAIT 0x%x",
- cx->address);
+ snprintf(cx->desc, ACPI_CX_DESC_LEN, "ACPI FFH INTEL MWAIT 0x%x (0x%x)",
+ hint, cx->address);

out:
set_cpus_allowed(current, saved_mask);

Rgds
--
-- Pierre Ossman

Linux kernel, MMC maintainer http://www.kernel.org
PulseAudio, core developer http://pulseaudio.org
rdesktop, core developer http://www.rdesktop.org


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