On Fri, Aug 1, 2025 at 12:15 AM Alexei Starovoitov
[off-list ref] wrote:

On Mon, Jul 28, 2025 at 2:20 AM Menglong Dong [off-list ref] wrote:

quoted

On Thu, Jul 17, 2025 at 6:35 AM Alexei Starovoitov
[off-list ref] wrote:

quoted

On Wed, Jul 16, 2025 at 11:24 AM Peter Zijlstra [off-list ref] wrote:

quoted

On Wed, Jul 16, 2025 at 09:56:11AM -0700, Alexei Starovoitov wrote:

quoted

Maybe Peter has better ideas ?

Is it possible to express runqueues::nr_pinned as an alias?

extern unsigned int __attribute__((alias("runqueues.nr_pinned"))) this_nr_pinned;

And use:

        __this_cpu_inc(&this_nr_pinned);


This syntax doesn't actually seem to work; but can we construct
something like that?

Yeah. Iant is right. It's a string and not a pointer dereference.
It never worked.

Few options:

1.
 struct rq {
+#ifdef CONFIG_SMP
+       unsigned int            nr_pinned;
+#endif
        /* runqueue lock: */
        raw_spinlock_t          __lock;

@@ -1271,9 +1274,6 @@ struct rq {
        struct cpuidle_state    *idle_state;
 #endif

-#ifdef CONFIG_SMP
-       unsigned int            nr_pinned;
-#endif

but ugly...

2.
static unsigned int nr_pinned_offset __ro_after_init __used;
RUNTIME_CONST(nr_pinned_offset, nr_pinned_offset)

overkill for what's needed

3.
OFFSET(RQ_nr_pinned, rq, nr_pinned);
then
#include <generated/asm-offsets.h>

imo the best.

I had a try. The struct rq is not visible to asm-offsets.c, so we
can't define it in arch/xx/kernel/asm-offsets.c. Do you mean
to define a similar rq-offsets.c in kernel/sched/ ? It will be more
complex than the way 2, and I think the second way 2 is
easier :/

2 maybe easier, but it's an overkill.
I still think asm-offset is cleaner.
arch/xx shouldn't be used, of course, since this nr_pinned should
be generic for all archs.
We can do something similar to drivers/memory/emif-asm-offsets.c

Great, I'll have a try on this way!

and do that within kernel/sched/.
rq-offsets.c as you said.
It will generate rq-offsets.h in a build dir that can be #include-d.

I thought about another alternative (as a derivative of 1):
split nr_pinned from 'struct rq' into its own per-cpu variable,
but I don't think that will work, since rq_has_pinned_tasks()
doesn't always operate on this_rq().
So the acceptable choices are realistically 1 and 3 and
rq-offsets.c seems cleaner.
Pls give it another try.