| 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
| ||
|
Message-ID: <20110907145421.GA32577@linux.vnet.ibm.com>
Date: Wed, 7 Sep 2011 20:24:21 +0530
From: Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
To: Paul Turner <pjt@...gle.com>
Cc: Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
Vladimir Davydov <vdavydov@...allels.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Bharata B Rao <bharata@...ux.vnet.ibm.com>,
Dhaval Giani <dhaval.giani@...il.com>,
Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
Ingo Molnar <mingo@...e.hu>,
Pavel Emelianov <xemul@...allels.com>
Subject: Re: CFS Bandwidth Control - Test results of cgroups tasks pinned vs
unpinned
* Paul Turner <pjt@...gle.com> [2011-06-21 12:48:17]:
> Hi Kamalesh,
>
> Can you see what things look like under v7?
>
> There's been a few improvements to quota re-distribution that should
> hopefully help your test case.
>
> The remaining idle% I see on my machines appear to be a product of
> load-balancer inefficiency.
which is quite a complex problem to solve! I am still surprised that
we can't handle 32 cpuhogs on a 16-cpu system very easily. The tasks seem to
hop around madly rather than settle down as 2 tasks/cpu. Kamalesh, can you post
the exact count of migrations we saw on latest tip over a 20-sec window?
Anyway, here's a "hack" to minimize the idle time induced due to load-balance
issues. It brings down idle time from 7+% to ~0% ..I am not too happy about
this, but I don't see any other simpler solutions to solve the idle time issue
completely (other than making load-balancer completely fair!).
--
Fix excessive idle time reported when cgroups are capped. The patch
introduces the notion of "steal" (or "grace") time which is the surplus
time/bandwidth each cgroup is allowed to consume, subject to a maximum
steal time (sched_cfs_max_steal_time_us). Cgroups are allowed this "steal"
or "grace" time when the lone task running on a cpu is about to be throttled.
Signed-off-by: Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
Index: linux-3.1-rc4/include/linux/sched.h
===================================================================
--- linux-3.1-rc4.orig/include/linux/sched.h 2011-09-07 14:57:49.529602231 +0800
+++ linux-3.1-rc4/include/linux/sched.h 2011-09-07 14:58:49.952418107 +0800
@@ -2042,6 +2042,7 @@ static inline void sched_autogroup_exit(
#ifdef CONFIG_CFS_BANDWIDTH
extern unsigned int sysctl_sched_cfs_bandwidth_slice;
+extern unsigned int sysctl_sched_cfs_max_steal_time;
#endif
#ifdef CONFIG_RT_MUTEXES
Index: linux-3.1-rc4/kernel/sched.c
===================================================================
--- linux-3.1-rc4.orig/kernel/sched.c 2011-09-07 14:57:49.532854588 +0800
+++ linux-3.1-rc4/kernel/sched.c 2011-09-07 14:58:49.955453578 +0800
@@ -254,7 +254,7 @@ struct cfs_bandwidth {
#ifdef CONFIG_CFS_BANDWIDTH
raw_spinlock_t lock;
ktime_t period;
- u64 quota, runtime;
+ u64 quota, runtime, steal_time;
s64 hierarchal_quota;
u64 runtime_expires;
Index: linux-3.1-rc4/kernel/sched_fair.c
===================================================================
--- linux-3.1-rc4.orig/kernel/sched_fair.c 2011-09-07 14:57:49.533644483 +0800
+++ linux-3.1-rc4/kernel/sched_fair.c 2011-09-07 15:16:09.338824132 +0800
@@ -101,6 +101,18 @@ unsigned int __read_mostly sysctl_sched_
* default: 5 msec, units: microseconds
*/
unsigned int sysctl_sched_cfs_bandwidth_slice = 5000UL;
+
+/*
+ * "Surplus" quota given to a cgroup to prevent a CPU from becoming idle.
+ *
+ * This would have been unnecessary had the load-balancer been "ideal" in
+ * loading tasks uniformly across all CPUs, which would have allowed
+ * all cgroups to claim their "quota" completely. In the absence of an
+ * "ideal" load-balancer, cgroups are unable to utilize their quota, leading
+ * to unexpected idle time. This knob allows a CPU to keep running a
+ * task beyond its throttled point before becoming idle.
+ */
+unsigned int sysctl_sched_cfs_max_steal_time = 100000UL;
#endif
static const struct sched_class fair_sched_class;
@@ -1288,6 +1300,11 @@ static inline u64 sched_cfs_bandwidth_sl
return (u64)sysctl_sched_cfs_bandwidth_slice * NSEC_PER_USEC;
}
+static inline u64 sched_cfs_max_steal_time(void)
+{
+ return (u64)sysctl_sched_cfs_max_steal_time * NSEC_PER_USEC;
+}
+
/*
* Replenish runtime according to assigned quota and update expiration time.
* We use sched_clock_cpu directly instead of rq->clock to avoid adding
@@ -1303,6 +1320,7 @@ static void __refill_cfs_bandwidth_runti
return;
now = sched_clock_cpu(smp_processor_id());
+ cfs_b->steal_time = 0;
cfs_b->runtime = cfs_b->quota;
cfs_b->runtime_expires = now + ktime_to_ns(cfs_b->period);
}
@@ -1337,6 +1355,12 @@ static int assign_cfs_rq_runtime(struct
cfs_b->runtime -= amount;
cfs_b->idle = 0;
}
+
+ if (!amount && rq_of(cfs_rq)->nr_running == 1 &&
+ cfs_b->steal_time < sched_cfs_max_steal_time()) {
+ amount = min_amount;
+ cfs_b->steal_time += amount;
+ }
}
expires = cfs_b->runtime_expires;
raw_spin_unlock(&cfs_b->lock);
@@ -1378,7 +1402,8 @@ static void expire_cfs_rq_runtime(struct
* whether the global deadline has advanced.
*/
- if ((s64)(cfs_rq->runtime_expires - cfs_b->runtime_expires) >= 0) {
+ if ((s64)(cfs_rq->runtime_expires - cfs_b->runtime_expires) >= 0 ||
+ (rq_of(cfs_rq)->nr_running == 1 && cfs_b->steal_time < sched_cfs_max_steal_time())) {
/* extend local deadline, drift is bounded above by 2 ticks */
cfs_rq->runtime_expires += TICK_NSEC;
} else {
Index: linux-3.1-rc4/kernel/sysctl.c
===================================================================
--- linux-3.1-rc4.orig/kernel/sysctl.c 2011-09-07 14:57:49.534454409 +0800
+++ linux-3.1-rc4/kernel/sysctl.c 2011-09-07 14:58:49.958452846 +0800
@@ -388,6 +388,14 @@ static struct ctl_table kern_table[] = {
.proc_handler = proc_dointvec_minmax,
.extra1 = &one,
},
+ {
+ .procname = "sched_cfs_max_steal_time_us",
+ .data = &sysctl_sched_cfs_max_steal_time,
+ .maxlen = sizeof(unsigned int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = &one,
+ },
#endif
#ifdef CONFIG_PROVE_LOCKING
{
--
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/
Powered by blists - more mailing lists