linux-kernel - [RFC PATCH v4 05/28] sched: Add hysteresis to switch a task's preferred LLC

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <e51f8a6e172606d520c91c94c0c14b045639217e.1754712565.git.tim.c.chen@linux.intel.com>
Date: Sat,  9 Aug 2025 13:02:18 +0800
From: Chen Yu <yu.c.chen@...el.com>
To: Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	K Prateek Nayak <kprateek.nayak@....com>,
	"Gautham R . Shenoy" <gautham.shenoy@....com>
Cc: Vincent Guittot <vincent.guittot@...aro.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	Libo Chen <libo.chen@...cle.com>,
	Madadi Vineeth Reddy <vineethr@...ux.ibm.com>,
	Hillf Danton <hdanton@...a.com>,
	Shrikanth Hegde <sshegde@...ux.ibm.com>,
	Jianyong Wu <jianyong.wu@...look.com>,
	Yangyu Chen <cyy@...self.name>,
	Tingyin Duan <tingyin.duan@...il.com>,
	Vern Hao <vernhao@...cent.com>,
	Len Brown <len.brown@...el.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Aubrey Li <aubrey.li@...el.com>,
	Zhao Liu <zhao1.liu@...el.com>,
	Chen Yu <yu.chen.surf@...il.com>,
	Chen Yu <yu.c.chen@...el.com>,
	linux-kernel@...r.kernel.org
Subject: [RFC PATCH v4 05/28] sched: Add hysteresis to switch a task's preferred LLC

From: Tim Chen <tim.c.chen@...ux.intel.com>

Switching a process's preferred LLC generates lots of task
migrations across LLCs. To avoid frequent switches
of home LLC, implement the following policy:

1. Require a 2x occ change threshold to switch preferred LLC
2. Don't discard preferred LLC for a task

Signed-off-by: Tim Chen <tim.c.chen@...ux.intel.com>
---
 kernel/sched/fair.c | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index a7be5c5ecba3..9e3c6f0eb934 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1175,6 +1175,14 @@ static s64 update_curr_se(struct rq *rq, struct sched_entity *curr)
 #define EPOCH_PERIOD	(HZ/100)	/* 10 ms */
 #define EPOCH_OLD	5		/* 50 ms */
 
+static int llc_id(int cpu)
+{
+	if (cpu < 0)
+		return -1;
+
+	return per_cpu(sd_llc_id, cpu);
+}
+
 void mm_init_sched(struct mm_struct *mm, struct mm_sched __percpu *_pcpu_sched)
 {
 	unsigned long epoch;
@@ -1307,6 +1315,7 @@ static void __no_profile task_cache_work(struct callback_head *work)
 	struct task_struct *p = current;
 	struct mm_struct *mm = p->mm;
 	unsigned long m_a_occ = 0;
+	unsigned long last_m_a_occ = 0;
 	int cpu, m_a_cpu = -1;
 	cpumask_var_t cpus;
 
@@ -1345,11 +1354,13 @@ static void __no_profile task_cache_work(struct callback_head *work)
 					     per_cpu(sd_llc_id, i), occ, m_occ, m_cpu, nr);
 			}
 
-			a_occ /= nr;
+			// a_occ /= nr;
 			if (a_occ > m_a_occ) {
 				m_a_occ = a_occ;
 				m_a_cpu = m_cpu;
 			}
+			if (llc_id(cpu) == llc_id(mm->mm_sched_cpu))
+				last_m_a_occ = a_occ;
 
 			trace_printk("(%d) a_occ: %ld m_a_occ: %ld\n",
 				     per_cpu(sd_llc_id, cpu), a_occ, m_a_occ);
@@ -1363,13 +1374,10 @@ static void __no_profile task_cache_work(struct callback_head *work)
 		}
 	}
 
-	/*
-	 * If the max average cache occupancy is 'small' we don't care.
-	 */
-	if (m_a_occ < (NICE_0_LOAD >> EPOCH_OLD))
-		m_a_cpu = -1;
-
-	mm->mm_sched_cpu = m_a_cpu;
+	if (m_a_occ > (2 * last_m_a_occ)) {
+		/* avoid the bouncing of mm_sched_cpu */
+		mm->mm_sched_cpu = m_a_cpu;
+	}
 
 	free_cpumask_var(cpus);
 }
-- 
2.25.1