Hi Borislav,
Thank you very much for your review.
On 12/7/2020 10:29 AM, Borislav Petkov wrote:
On Thu, Dec 03, 2020 at 03:25:48PM -0800, Reinette Chatre wrote:
From: Fenghua Yu <fenghua.yu@xxxxxxxxx>
The code of setting the CPU on which a task is running in a CPU mask is
moved into a couple of helpers.
Pls read section "2) Describe your changes" in
Documentation/process/submitting-patches.rst for more details.
More specifically:
"Describe your changes in imperative mood, e.g. "make xyzzy do frotz"
instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy
to do frotz", as if you are giving orders to the codebase to change
its behaviour."
The new helper task_on_cpu() will be reused shortly.
"reused shortly"? I don't think so.
How about:
"Move the setting of the CPU on which a task is running in a CPU mask
into a couple of helpers.
There is no functional change. This is a preparatory change for the fix
in the following patch from where the Fixes tag is copied."
Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Signed-off-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Fixes?
I guess the same commit from the other two:
Fixes: e02737d5b826 ("x86/intel_rdt: Add tasks files")
?
Correct. I will add it. The addition to the commit message above aims to
explain a Fixes tag to a patch with no functional changes.
---
arch/x86/kernel/cpu/resctrl/rdtgroup.c | 47 +++++++++++++++++++-------
1 file changed, 34 insertions(+), 13 deletions(-)
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 6f4ca4bea625..68db7d2dec8f 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -525,6 +525,38 @@ static void rdtgroup_remove(struct rdtgroup *rdtgrp)
kfree(rdtgrp);
}
+#ifdef CONFIG_SMP
+/* Get the CPU if the task is on it. */
+static bool task_on_cpu(struct task_struct *t, int *cpu)
+{
+ /*
+ * This is safe on x86 w/o barriers as the ordering of writing to
+ * task_cpu() and t->on_cpu is reverse to the reading here. The
+ * detection is inaccurate as tasks might move or schedule before
+ * the smp function call takes place. In such a case the function
+ * call is pointless, but there is no other side effect.
+ */
+ if (t->on_cpu) {
+ *cpu = task_cpu(t);
Why have an I/O parameter when you can make it simply:
static int task_on_cpu(struct task_struct *t)
{
if (t->on_cpu)
return task_cpu(t);
return -1;
}
+
+ return true;
+ }
+
+ return false;
+}
+
+static void set_task_cpumask(struct task_struct *t, struct cpumask *mask)
+{
+ int cpu;
+
+ if (mask && task_on_cpu(t, &cpu))
+ cpumask_set_cpu(cpu, mask);
And that you can turn into:
if (!mask)
return;
cpu = task_on_cpu(t);
if (cpu < 0)
return;
cpumask_set_cpu(cpu, mask);
Readable and simple.
Hmm?
Will do. Thank you very much.
Reinette
