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 <kenchen@google.com> Cc: Paul Menage <menage@google.com> Cc: Li Zefan <lizf@cn.fujitsu.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
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@ -9275,6 +9275,41 @@ cpuacct_destroy(struct cgroup_subsys *ss, struct cgroup *cgrp)
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kfree(ca);
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}
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static u64 cpuacct_cpuusage_read(struct cpuacct *ca, int cpu)
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{
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u64 *cpuusage = percpu_ptr(ca->cpuusage, cpu);
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u64 data;
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#ifndef CONFIG_64BIT
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/*
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* Take rq->lock to make 64-bit read safe on 32-bit platforms.
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*/
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spin_lock_irq(&cpu_rq(cpu)->lock);
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data = *cpuusage;
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spin_unlock_irq(&cpu_rq(cpu)->lock);
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#else
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data = *cpuusage;
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#endif
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return data;
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}
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static void cpuacct_cpuusage_write(struct cpuacct *ca, int cpu, u64 val)
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{
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u64 *cpuusage = percpu_ptr(ca->cpuusage, cpu);
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#ifndef CONFIG_64BIT
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/*
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* Take rq->lock to make 64-bit write safe on 32-bit platforms.
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*/
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spin_lock_irq(&cpu_rq(cpu)->lock);
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*cpuusage = val;
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spin_unlock_irq(&cpu_rq(cpu)->lock);
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#else
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*cpuusage = val;
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#endif
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}
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/* return total cpu usage (in nanoseconds) of a group */
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static u64 cpuusage_read(struct cgroup *cgrp, struct cftype *cft)
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{
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@ -9282,17 +9317,8 @@ static u64 cpuusage_read(struct cgroup *cgrp, struct cftype *cft)
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u64 totalcpuusage = 0;
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int i;
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for_each_possible_cpu(i) {
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u64 *cpuusage = percpu_ptr(ca->cpuusage, i);
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/*
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* Take rq->lock to make 64-bit addition safe on 32-bit
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* platforms.
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*/
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spin_lock_irq(&cpu_rq(i)->lock);
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totalcpuusage += *cpuusage;
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spin_unlock_irq(&cpu_rq(i)->lock);
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}
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for_each_present_cpu(i)
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totalcpuusage += cpuacct_cpuusage_read(ca, i);
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return totalcpuusage;
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}
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@ -9309,13 +9335,9 @@ static int cpuusage_write(struct cgroup *cgrp, struct cftype *cftype,
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goto out;
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}
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for_each_possible_cpu(i) {
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u64 *cpuusage = percpu_ptr(ca->cpuusage, i);
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for_each_present_cpu(i)
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cpuacct_cpuusage_write(ca, i, 0);
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spin_lock_irq(&cpu_rq(i)->lock);
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*cpuusage = 0;
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spin_unlock_irq(&cpu_rq(i)->lock);
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}
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out:
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return err;
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}
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