On 11/19/25 1:53 PM, Greg KH wrote:
On Wed, Nov 19, 2025 at 01:38:24PM +0530, Shrikanth Hegde wrote:
Hi Greg.
On 11/19/25 1:12 PM, Greg KH wrote:
On Wed, Nov 19, 2025 at 11:50:59AM +0530, Shrikanth Hegde wrote:
This is helper patch which could be used to set the range of CPUs as
paravirt. One could make use of this for quick testing of this infra
instead of writing arch specific code.
This is currently not meant be merged, since paravirt sysfs file is meant
to be Read-Only.
echo 100-200,600-700 > /sys/devices/system/cpu/paravirt
cat /sys/devices/system/cpu/paravirt
100-200,600-700
echo > /sys/devices/system/cpu/paravirt
cat /sys/devices/system/cpu/paravirt
Signed-off-by: Shrikanth Hegde <[email protected]>
---
drivers/base/cpu.c | 48 ++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 46 insertions(+), 2 deletions(-)
diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index 59ceae217b22..043e4f4ce1a9 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -375,12 +375,57 @@ static int cpu_uevent(const struct device *dev, struct
kobj_uevent_env *env)
#endif
#ifdef CONFIG_PARAVIRT
+static ssize_t store_paravirt_cpus(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf, size_t count)
+{
+ cpumask_var_t temp_mask;
+ int retval = 0;
+
+ if (!alloc_cpumask_var(&temp_mask, GFP_KERNEL))
+ return -ENOMEM;
+
+ retval = cpulist_parse(buf, temp_mask);
+ if (retval)
+ goto free_mask;
+
+ /* ALL cpus can't be marked as paravirt */
+ if (cpumask_equal(temp_mask, cpu_online_mask)) {
+ retval = -EINVAL;
+ goto free_mask;
+ }
+ if (cpumask_weight(temp_mask) > num_online_cpus()) {
+ retval = -EINVAL;
+ goto free_mask;
+ }
+
+ /* No more paravirt cpus */
+ if (cpumask_empty(temp_mask)) {
+ cpumask_copy((struct cpumask *)&__cpu_paravirt_mask, temp_mask);
+ } else {
+ cpumask_copy((struct cpumask *)&__cpu_paravirt_mask, temp_mask);
+
+ /* Enable tick on nohz_full cpu */
+ int cpu;
+ for_each_cpu(cpu, temp_mask) {
+ if (tick_nohz_full_cpu(cpu))
+ tick_nohz_dep_set_cpu(cpu, TICK_DEP_BIT_SCHED);
+ }
+ }
+
+ retval = count;
+
+free_mask:
+ free_cpumask_var(temp_mask);
+ return retval;
+}
+
static ssize_t print_paravirt_cpus(struct device *dev,
struct device_attribute *attr, char *buf)
{
return sysfs_emit(buf, "%*pbl\n", cpumask_pr_args(cpu_paravirt_mask));
}
-static DEVICE_ATTR(paravirt, 0444, print_paravirt_cpus, NULL);
+static DEVICE_ATTR(paravirt, 0644, print_paravirt_cpus, store_paravirt_cpus);
DEVICE_ATTR_RW()?
ok.
And where is the documentation update for this sysfs file change?
[RFC PATCH v4 11/17] has the documentation of this sysfs file.
https://lore.kernel.org/all/[email protected]/
So a rfc patch has the documentation for a change that you don't want to
have applied? This is an odd series, how are we supposed to review
this?
I added the documentation for sysfs file as the file is read only. The last two
patch are debug patches. So i didn't update the documentation saying it can be
written
too. I hope this clears the doubts.
This is a helper patch. This helps to verify functionality of any combination
of CPUs being marked as paravirt which helped me to test some corner cases.
I don't think I have ever seen a "helper patch" to know what to do with
it :(
Sorry for confusion with the name.
All I wanted to say there was it is debug patch one could use.
Would [RFC PATCH 16/17][DEBUG] would have been a better name?
