From 720f54988e17b33f3f477010b3a68ee872d20d5a Mon Sep 17 00:00:00 2001 From: Ken Chen Date: Mon, 15 Dec 2008 22:02:01 -0800 Subject: [PATCH] sched, cpuacct: refactoring cpuusage_read / cpuusage_write Impact: micro-optimize the code on 64-bit architectures In the thread regarding to 'export percpu cpuacct cgroup stats' http://lkml.org/lkml/2008/12/7/13 akpm pointed out that current cpuacct code is inefficient. This patch refactoring the following: * make cpu_rq locking only on 32-bit * change iterator to each_present_cpu instead of each_possible_cpu to make it hotplug friendly. It's a bit of code churn, but I was rewarded with 160 byte code size saving on x86-64 arch and zero code size change on i386. Signed-off-by: Ken Chen Cc: Paul Menage Cc: Li Zefan Signed-off-by: Ingo Molnar --- kernel/sched.c | 56 +++++++++++++++++++++++++++++++++++--------------- 1 file changed, 39 insertions(+), 17 deletions(-) diff --git a/kernel/sched.c b/kernel/sched.c index 88215066efa..41b7e2d524d 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -9275,6 +9275,41 @@ cpuacct_destroy(struct cgroup_subsys *ss, struct cgroup *cgrp) kfree(ca); } +static u64 cpuacct_cpuusage_read(struct cpuacct *ca, int cpu) +{ + u64 *cpuusage = percpu_ptr(ca->cpuusage, cpu); + u64 data; + +#ifndef CONFIG_64BIT + /* + * Take rq->lock to make 64-bit read safe on 32-bit platforms. + */ + spin_lock_irq(&cpu_rq(cpu)->lock); + data = *cpuusage; + spin_unlock_irq(&cpu_rq(cpu)->lock); +#else + data = *cpuusage; +#endif + + return data; +} + +static void cpuacct_cpuusage_write(struct cpuacct *ca, int cpu, u64 val) +{ + u64 *cpuusage = percpu_ptr(ca->cpuusage, cpu); + +#ifndef CONFIG_64BIT + /* + * Take rq->lock to make 64-bit write safe on 32-bit platforms. + */ + spin_lock_irq(&cpu_rq(cpu)->lock); + *cpuusage = val; + spin_unlock_irq(&cpu_rq(cpu)->lock); +#else + *cpuusage = val; +#endif +} + /* return total cpu usage (in nanoseconds) of a group */ static u64 cpuusage_read(struct cgroup *cgrp, struct cftype *cft) { @@ -9282,17 +9317,8 @@ static u64 cpuusage_read(struct cgroup *cgrp, struct cftype *cft) u64 totalcpuusage = 0; int i; - for_each_possible_cpu(i) { - u64 *cpuusage = percpu_ptr(ca->cpuusage, i); - - /* - * Take rq->lock to make 64-bit addition safe on 32-bit - * platforms. - */ - spin_lock_irq(&cpu_rq(i)->lock); - totalcpuusage += *cpuusage; - spin_unlock_irq(&cpu_rq(i)->lock); - } + for_each_present_cpu(i) + totalcpuusage += cpuacct_cpuusage_read(ca, i); return totalcpuusage; } @@ -9309,13 +9335,9 @@ static int cpuusage_write(struct cgroup *cgrp, struct cftype *cftype, goto out; } - for_each_possible_cpu(i) { - u64 *cpuusage = percpu_ptr(ca->cpuusage, i); + for_each_present_cpu(i) + cpuacct_cpuusage_write(ca, i, 0); - spin_lock_irq(&cpu_rq(i)->lock); - *cpuusage = 0; - spin_unlock_irq(&cpu_rq(i)->lock); - } out: return err; }