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
| ||
|
Date: Mon, 18 Jan 2010 15:41:42 +1100 From: Anton Blanchard <anton@...ba.org> To: Bharata B Rao <bharata@...ux.vnet.ibm.com> Cc: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>, Ingo Molnar <mingo@...e.hu>, Balbir Singh <balbir@...ux.vnet.ibm.com>, mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org, a.p.zijlstra@...llo.nl, schwidefsky@...ibm.com, balajirrao@...il.com, dhaval@...ux.vnet.ibm.com, tglx@...utronix.de, kamezawa.hiroyu@...fujitsu.com, akpm@...ux-foundation.org, Tony Luck <tony.luck@...el.com>, Fenghua Yu <fenghua.yu@...el.com>, Heiko Carstens <heiko.carstens@...ibm.com>, linux390@...ibm.com Subject: [PATCH] sched: cpuacct: Use bigger percpu counter batch values for stats counters Hi, Another try at this percpu_counter batch issue with CONFIG_VIRT_CPU_ACCOUNTING and CONFIG_CGROUP_CPUACCT enabled. Thoughts? -- When CONFIG_VIRT_CPU_ACCOUNTING and CONFIG_CGROUP_CPUACCT are enabled we can call cpuacct_update_stats with values much larger than percpu_counter_batch. This means the call to percpu_counter_add will always add to the global count which is protected by a spinlock and we end up with a global spinlock in the scheduler. Based on an idea by KOSAKI Motohiro, this patch scales the batch value by cputime_one_jiffy such that we have the same batch limit as we would if CONFIG_VIRT_CPU_ACCOUNTING was disabled. His patch did this once at boot but that initialisation happened too early on PowerPC (before time_init) and it was never updated at runtime as a result of a hotplug cpu add/remove. This patch instead scales percpu_counter_batch by cputime_one_jiffy at runtime, which keeps the batch correct even after cpu hotplug operations. We cap it at INT_MAX in case of overflow. For architectures that do not support CONFIG_VIRT_CPU_ACCOUNTING, cputime_one_jiffy is the constant 1 and gcc is smart enough to optimise min(s32 percpu_counter_batch, INT_MAX) to just percpu_counter_batch at least on x86 and PowerPC. So there is no need to add an #ifdef. On a 64 thread PowerPC box with CONFIG_VIRT_CPU_ACCOUNTING and CONFIG_CGROUP_CPUACCT enabled, a context switch microbenchmark is 234x faster and almost matches a CONFIG_CGROUP_CPUACCT disabled kernel: CONFIG_CGROUP_CPUACCT disabled: 16906698 ctx switches/sec CONFIG_CGROUP_CPUACCT enabled: 61720 ctx switches/sec CONFIG_CGROUP_CPUACCT + patch: 16663217 ctx switches/sec Tested with: wget http://ozlabs.org/~anton/junkcode/context_switch.c make context_switch for i in `seq 0 63`; do taskset -c $i ./context_switch & done vmstat 1 Signed-off-by: Anton Blanchard <anton@...ba.org> --- Note: ccing ia64 and s390 who have not yet added code to statically initialise cputime_one_jiffy at boot. See a42548a18866e87092db93b771e6c5b060d78401 (cputime: Optimize jiffies_to_cputime(1) for details). Adding this would help optimise not only this patch but many other areas of the scheduler when CONFIG_VIRT_CPU_ACCOUNTING is enabled. Index: linux.trees.git/kernel/sched.c =================================================================== --- linux.trees.git.orig/kernel/sched.c 2010-01-18 14:27:12.000000000 +1100 +++ linux.trees.git/kernel/sched.c 2010-01-18 15:21:59.000000000 +1100 @@ -10894,6 +10894,7 @@ static void cpuacct_update_stats(struct enum cpuacct_stat_index idx, cputime_t val) { struct cpuacct *ca; + int batch; if (unlikely(!cpuacct_subsys.active)) return; @@ -10901,8 +10902,9 @@ static void cpuacct_update_stats(struct rcu_read_lock(); ca = task_ca(tsk); + batch = min_t(long, percpu_counter_batch * cputime_one_jiffy, INT_MAX); do { - percpu_counter_add(&ca->cpustat[idx], val); + __percpu_counter_add(&ca->cpustat[idx], val, batch); ca = ca->parent; } while (ca); rcu_read_unlock(); -- 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