* [PATCH 2/2] powerpc: Use smt_snooze_delay=-1 to always busy loop
2010-05-17 6:01 [PATCH 1/2] powerpc: Remove ibm,smt-snooze-delay OF property Anton Blanchard
@ 2010-05-17 6:02 ` Anton Blanchard
0 siblings, 0 replies; 2+ messages in thread
From: Anton Blanchard @ 2010-05-17 6:02 UTC (permalink / raw)
To: benh, nfont; +Cc: linuxppc-dev
Right now if we want to busy loop and not give up any time to the hypervisor
we put a very large value into smt_snooze_delay. This is sometimes useful
when running a single partition and you want to avoid any latencies due
to the hypervisor or CPU power state transitions. While this works, it's a bit
ugly - how big a number is enough now we have NO_HZ and can be idle for a very
long time.
The patch below makes smt_snooze_delay signed, and a negative value means loop
forever:
echo -1 > /sys/devices/system/cpu/cpu0/smt_snooze_delay
This change shouldn't affect the existing userspace tools (eg ppc64_cpu), but
I'm cc-ing Nathan just to be sure.
Signed-off-by: Anton Blanchard <anton@samba.org>
---
Index: powerpc.git/arch/powerpc/kernel/sysfs.c
===================================================================
--- powerpc.git.orig/arch/powerpc/kernel/sysfs.c 2010-05-17 15:18:24.164704601 +1000
+++ powerpc.git/arch/powerpc/kernel/sysfs.c 2010-05-17 15:18:26.207205125 +1000
@@ -35,7 +35,7 @@ static DEFINE_PER_CPU(struct cpu, cpu_de
#ifdef CONFIG_PPC64
/* Time in microseconds we delay before sleeping in the idle loop */
-DEFINE_PER_CPU(unsigned long, smt_snooze_delay) = { 100 };
+DEFINE_PER_CPU(long, smt_snooze_delay) = { 100 };
static ssize_t store_smt_snooze_delay(struct sys_device *dev,
struct sysdev_attribute *attr,
@@ -44,9 +44,9 @@ static ssize_t store_smt_snooze_delay(st
{
struct cpu *cpu = container_of(dev, struct cpu, sysdev);
ssize_t ret;
- unsigned long snooze;
+ long snooze;
- ret = sscanf(buf, "%lu", &snooze);
+ ret = sscanf(buf, "%ld", &snooze);
if (ret != 1)
return -EINVAL;
@@ -61,7 +61,7 @@ static ssize_t show_smt_snooze_delay(str
{
struct cpu *cpu = container_of(dev, struct cpu, sysdev);
- return sprintf(buf, "%lu\n", per_cpu(smt_snooze_delay, cpu->sysdev.id));
+ return sprintf(buf, "%ld\n", per_cpu(smt_snooze_delay, cpu->sysdev.id));
}
static SYSDEV_ATTR(smt_snooze_delay, 0644, show_smt_snooze_delay,
@@ -70,15 +70,14 @@ static SYSDEV_ATTR(smt_snooze_delay, 064
static int __init setup_smt_snooze_delay(char *str)
{
unsigned int cpu;
- int snooze;
+ long snooze;
if (!cpu_has_feature(CPU_FTR_SMT))
return 1;
- if (get_option(&str, &snooze)) {
- for_each_possible_cpu(cpu)
- per_cpu(smt_snooze_delay, cpu) = snooze;
- }
+ snooze = simple_strtol(str, NULL, 10);
+ for_each_possible_cpu(cpu)
+ per_cpu(smt_snooze_delay, cpu) = snooze;
return 1;
}
Index: powerpc.git/arch/powerpc/platforms/pseries/setup.c
===================================================================
--- powerpc.git.orig/arch/powerpc/platforms/pseries/setup.c 2010-05-17 15:05:29.827204407 +1000
+++ powerpc.git/arch/powerpc/platforms/pseries/setup.c 2010-05-17 15:18:26.207205125 +1000
@@ -496,13 +496,14 @@ static int __init pSeries_probe(void)
}
-DECLARE_PER_CPU(unsigned long, smt_snooze_delay);
+DECLARE_PER_CPU(long, smt_snooze_delay);
static void pseries_dedicated_idle_sleep(void)
{
unsigned int cpu = smp_processor_id();
unsigned long start_snooze;
unsigned long in_purr, out_purr;
+ long snooze = __get_cpu_var(smt_snooze_delay);
/*
* Indicate to the HV that we are idle. Now would be
@@ -517,13 +518,12 @@ static void pseries_dedicated_idle_sleep
* has been checked recently. If we should poll for a little
* while, do so.
*/
- if (__get_cpu_var(smt_snooze_delay)) {
- start_snooze = get_tb() +
- __get_cpu_var(smt_snooze_delay) * tb_ticks_per_usec;
+ if (snooze) {
+ start_snooze = get_tb() + snooze * tb_ticks_per_usec;
local_irq_enable();
set_thread_flag(TIF_POLLING_NRFLAG);
- while (get_tb() < start_snooze) {
+ while ((snooze < 0) || (get_tb() < start_snooze)) {
if (need_resched() || cpu_is_offline(cpu))
goto out;
ppc64_runlatch_off();
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