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.
>
> 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")
?
> ---
> 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?
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
