The patch below does not apply to the 4.4-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@xxxxxxxxxxxxxxx>.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
>From a02f6d42357acf6e5de6ffc728e6e77faf3ad217 Mon Sep 17 00:00:00 2001
From: Joel Stanley <joel@xxxxxxxxx>
Date: Wed, 2 Sep 2020 09:30:11 +0930
Subject: [PATCH] powerpc: Warn about use of smt_snooze_delay
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: 3fa8cad82b94 ("powerpc/pseries/cpuidle: smt-snooze-delay cleanup.")
Cc: stable@xxxxxxxxxxxxxxx # v3.14
Signed-off-by: Joel Stanley <joel@xxxxxxxxx>
Acked-by: Gautham R. Shenoy <ego@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20200902000012.3440389-1-joel@xxxxxxxxx
diff --git a/arch/powerpc/kernel/sysfs.c b/arch/powerpc/kernel/sysfs.c
index 46b4ebc33db7..5dea98fa2f93 100644
--- a/arch/powerpc/kernel/sysfs.c
+++ b/arch/powerpc/kernel/sysfs.c
@@ -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);
