xiaomi-sm8450/android_kernel_xiaomi_sm8450
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

powerpc: Use smt_snooze_delay=-1 to always busy loop

Browse Source 
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>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This commit is contained in:
Anton Blanchard
2010-05-16 20:02:39 +00:00
committed by Benjamin Herrenschmidt
parent dd04c63c96
commit b878dc0059
2 changed files with 13 additions and 14 deletions
Download Patch File Download Diff File Expand all files Collapse all files

17
arch/powerpc/kernel/sysfs.c
View File

@@ -35,7 +35,7 @@ static DEFINE_PER_CPU(struct cpu, cpu_devices);
#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(struct sys_device *dev,
{
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(struct sys_device *dev,
{
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, 0644, show_smt_snooze_delay,
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;
}