Commit a02f6d42 authored by Joel Stanley's avatar Joel Stanley Committed by Michael Ellerman
Browse files

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: 3fa8cad8 ("powerpc/pseries/cpuidle: smt-snooze-delay cleanup.")
Cc: stable@vger.kernel.org # v3.14
Signed-off-by: default avatarJoel Stanley <joel@jms.id.au>
Acked-by: default avatarGautham R. Shenoy <ego@linux.vnet.ibm.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200902000012.3440389-1-joel@jms.id.au
parent 8f55984f

arch/powerpc/kernel/sysfs.c

+17 −25
Original line number Diff line number Diff line
@@ -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);

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