linux-kernel - Side effects of disabling SCHED_SOFTIRQ to trigger run_rebalance

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>] [day] [month] [year] [list]

Message-ID: <CAH83jXTx7OEYCFJx-hKA6P1v90MYNmNaE2N4m92RZgCc8Agh_g@mail.gmail.com>
Date:	Mon, 17 Sep 2012 16:54:19 +0800
From:	Xiong Wu <xiong.wu1981@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: Side effects of disabling SCHED_SOFTIRQ to trigger run_rebalance_domains

Hi all,

Since observed dead lock problem in sched run_rebalance_domains of
kernel 2.6.21.7, we just disabling SCHED_SOFTIRQ to trigger
run_rebalance_domains as one work around. The patch is as below:

--- kernel/sched.c      2012-06-29 23:17:34.000000000 +0800
+++ kernel-new/sched.c  2012-09-12 17:27:28.000000000 +0800
@@ -2940,7 +2940,7 @@ static void update_load(struct rq *this_
  * Balancing parameters are set up in arch_init_sched_domains.
  */
 static DEFINE_SPINLOCK(balancing);
-
+#if 0
 static void run_rebalance_domains(struct softirq_action *h)
 {
        int this_cpu = smp_processor_id(), balance = 1;
@@ -3001,6 +3001,7 @@ out:
        }
        this_rq->next_balance = next_balance;
 }
+#endif
 #else
 /*
  * on UP we do not need to balance between CPUs:
@@ -3230,9 +3231,11 @@ void scheduler_tick(void)
                task_running_tick(rq, p);
 #ifdef CONFIG_SMP
        update_load(rq);
+#if 0
        if (time_after_eq(jiffies, rq->next_balance))
                raise_softirq(SCHED_SOFTIRQ);
 #endif
+#endif
 }

 #if defined(CONFIG_PREEMPT) && defined(CONFIG_DEBUG_PREEMPT)
@@ -6766,9 +6769,11 @@ void __init sched_init(void)

        set_load_weight(&init_task);

+#if 0
 #ifdef CONFIG_SMP
        open_softirq(SCHED_SOFTIRQ, run_rebalance_domains, NULL);
 #endif
+#endif

 #ifdef CONFIG_RT_MUTEXES
        plist_head_init(&init_task.pi_waiters, &init_task.pi_lock);


Our experimentations and simulations that we have conducted so far did
not indicated any performance decrease due to disable re-balancing.
Since our system isn't always busy, the idle_balance can work well for
processes load balance instead of run_rebalance_domains.  However my
concern is if there is any side effects which I didn't consider.



Thanks,
Xiong
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/