sched/cache: Keep nr_pref_llc_running in the runnable domain, to fix LLC mis-scheduling buggrafted

alb_break_llc() decides whether to break LLC preference during active
load balance. It does so by testing that every runnable fair task on the
source rq prefers its LLC:

	env->src_rq->nr_pref_llc_running == env->src_rq->cfs.h_nr_runnable

But the two counters cover different sets. nr_pref_llc_running is updated
in account_llc_enqueue()/account_llc_dequeue(), next to cfs_rq->nr_queued,
so it follows queued tasks. h_nr_runnable is updated in set_delayed()/
clear_delayed() and drops delay-dequeued tasks.

So under DELAY_DEQUEUE, a preferring task that goes to sleep stays counted
in nr_pref_llc_running while h_nr_runnable falls. The equality then breaks,
alb_break_llc() returns false, and active balance is free to pull a task
off its preferred LLC. Active balance only moves runnable tasks, and this
is the only LLC check it consults: once the stopper runs, LBF_ACTIVE_LB
skips the per-task test in can_migrate_task(). The runnable set is the one
we want.

Fix it on the counter side. A task should be counted in
nr_pref_llc_running exactly while it is both queued on its preferred LLC
(pref_llc_queued) and runnable (!sched_delayed). Define that membership
once in task_pref_llc_runnable(), and adjust the counter only through
pref_llc_running_inc()/pref_llc_running_dec() from the four sites that
change either input: account_llc_enqueue(), account_llc_dequeue(),
set_delayed() and clear_delayed(). Gating every update on the same
predicate keeps the delay, wake and dequeue paths from double-counting
or underflowing; see the comments at those sites for the ordering.

nr_llc_running and sd->llc_counts are not touched and stay on queued
semantics.

Fixes: 714059f79ff0 ("sched/cache: Handle moving single tasks to/from their preferred LLC")
Closes: https://lore.kernel.org/lkml/20260827135000.735138-1-zhanxusheng@xiaomi.com/
Reported-by: Zhan Xusheng <zhanxusheng@xiaomi.com>
Suggested-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Kayra Cizmeci <kayracizmeci@gmail.com>
Cc: <stable@kernel.org> # v7.2.x
Link: https://patch.msgid.link/06af61afedac32e6477f57feb4d658f6c411c3af.1790035273.git.tim.c.chen@linux.intel.com

1 files changed, 44 insertions, 0 deletions

diff --git a/tools/perf/ui/keysyms.c b/tools/perf/ui/keysyms.c
new file mode 100644
index 000000000..b64564b07
--- /dev/null
+++ b/tools/perf/ui/keysyms.c
@@ -0,0 +1,44 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#include "keysyms.h"
+#include <linux/ctype.h>
+#include <linux/kernel.h>
+
+const char *key_name(int key, char *bf, size_t size)
+{
+	if (isprint(key)) {
+		scnprintf(bf, size, "%c", key); 
+	} else if (key < 32) {
+		scnprintf(bf, size, "Ctrl+%c", key + '@'); 
+	} else {
+		const char *name = NULL;
+
+		switch (key) {
+		case K_DOWN:	name = "Down";	    break;
+		case K_END:	name = "End";	    break;
+		case K_ENTER:	name = "Enter";	    break;
+		case K_ESC:	name = "ESC";	    break;
+		case K_F1:	name = "F1";	    break;
+		case K_HOME:	name = "Home";	    break;
+		case K_LEFT:	name = "Left";	    break;
+		case K_PGDN:	name = "PgDown";    break;
+		case K_PGUP:	name = "PgUp";	    break;
+		case K_RIGHT:	name = "Right";	    break;
+		case K_TAB:	name = "Tab";	    break;
+		case K_UNTAB:	name = "Untab";	    break;
+		case K_UP:	name = "Up";	    break;
+		case K_BKSPC:	name = "Backspace"; break;
+		case K_DEL:	name = "Del";	    break;
+		default:
+			if (key >= SL_KEY_F(1) && key <= SL_KEY_F(63))
+				scnprintf(bf, size, "F%d", key - SL_KEY_F(0));
+			else
+				scnprintf(bf, size, "Unknown (%d)", key);
+		}
+
+		if (name)
+			scnprintf(bf, size, "%s", name);
+	}
+
+	return bf;
+}