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Commit 720f5498 authored by Ken Chen's avatar Ken Chen Committed by Ingo Molnar
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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: default avatarKen Chen <kenchen@google.com>
Cc: Paul Menage <menage@google.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 34f28ecd

kernel/sched.c

+39 −17
Original line number Diff line number Diff line
@@ -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;

}