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powerpc: Warn about use of smt_snooze_delay

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It's not done anything for a long time. Save the percpu variable, and
emit a warning to remind users to not expect it to do anything.

This uses pr_warn_once instead of pr_warn_ratelimit as testing
'ppc64_cpu --smt=off' on a 24 core / 4 SMT system showed the warning
to be noisy, as the online/offline loop is slow.

Fixes: 3fa8cad82b ("powerpc/pseries/cpuidle: smt-snooze-delay cleanup.")
Cc: stable@vger.kernel.org # v3.14
Signed-off-by: Joel Stanley <joel@jms.id.au>
Acked-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200902000012.3440389-1-joel@jms.id.au
This commit is contained in:
Joel Stanley 2020-09-02 09:30:11 +09:30 committed by Michael Ellerman
parent 8f55984f53
commit a02f6d4235
1 changed files with 17 additions and 25 deletions
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42
arch/powerpc/kernel/sysfs.c
View File

@ -32,29 +32,27 @@
static DEFINE_PER_CPU(struct cpu, cpu_devices);
/*
* SMT snooze delay stuff, 64-bit only for now
*/
#ifdef CONFIG_PPC64
/* Time in microseconds we delay before sleeping in the idle loop */
static DEFINE_PER_CPU(long, smt_snooze_delay) = { 100 };
/*
* Snooze delay has not been hooked up since 3fa8cad82b94 ("powerpc/pseries/cpuidle:
* smt-snooze-delay cleanup.") and has been broken even longer. As was foretold in
* 2014:
*
* "ppc64_util currently utilises it. Once we fix ppc64_util, propose to clean
* up the kernel code."
*
* powerpc-utils stopped using it as of 1.3.8. At some point in the future this
* code should be removed.
*/
static ssize_t store_smt_snooze_delay(struct device *dev,
struct device_attribute *attr,
const char *buf,
size_t count)
{
struct cpu *cpu = container_of(dev, struct cpu, dev);
ssize_t ret;
long snooze;
ret = sscanf(buf, "%ld", &snooze);
if (ret != 1)
return -EINVAL;
per_cpu(smt_snooze_delay, cpu->dev.id) = snooze;
pr_warn_once("%s (%d) stored to unsupported smt_snooze_delay, which has no effect.\n",
current->comm, current->pid);
return count;
}
@ -62,9 +60,9 @@ static ssize_t show_smt_snooze_delay(struct device *dev,
struct device_attribute *attr,
char *buf)
{
struct cpu *cpu = container_of(dev, struct cpu, dev);
return sprintf(buf, "%ld\n", per_cpu(smt_snooze_delay, cpu->dev.id));
pr_warn_once("%s (%d) read from unsupported smt_snooze_delay\n",
current->comm, current->pid);
return sprintf(buf, "100\n");
}
static DEVICE_ATTR(smt_snooze_delay, 0644, show_smt_snooze_delay,
@ -72,16 +70,10 @@ static DEVICE_ATTR(smt_snooze_delay, 0644, show_smt_snooze_delay,
static int __init setup_smt_snooze_delay(char *str)
{
unsigned int cpu;
long snooze;
if (!cpu_has_feature(CPU_FTR_SMT))
return 1;
snooze = simple_strtol(str, NULL, 10);
for_each_possible_cpu(cpu)
per_cpu(smt_snooze_delay, cpu) = snooze;
pr_warn("smt-snooze-delay command line option has no effect\n");
return 1;
}
__setup("smt-snooze-delay=", setup_smt_snooze_delay);