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Commit 3d3a6021 authored by Nicholas Piggin's avatar Nicholas Piggin Committed by Michael Ellerman
Browse files

powerpc/pseries: lparcfg calculate PURR on demand 



For SPLPAR, lparcfg provides a sum of PURR registers for all CPUs.
Currently this is done by reading PURR in context switch and timer
interrupt, and storing that into a per-CPU variable. These are summed
to provide the value.

This does not work with all timer schemes (e.g., NO_HZ_FULL), and it
is sub-optimal for performance because it reads the PURR register on
every context switch, although that's been difficult to distinguish
from noise in the contxt_switch microbenchmark.

This patch implements the sum by calling a function on each CPU, to
read and add PURR values of each CPU.

Signed-off-by: default avatarNicholas Piggin <npiggin@gmail.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent 36d632ea

arch/powerpc/include/asm/time.h

+0 −8
Original line number Diff line number Diff line
@@ -196,14 +196,6 @@ extern u64 mulhdu(u64, u64); 
extern void div128_by_32(u64 dividend_high, u64 dividend_low,

			 unsigned divisor, struct div_result *dr);



/* Used to store Processor Utilization register (purr) values */



struct cpu_usage {

        u64 current_tb;  /* Holds the current purr register values */

};



DECLARE_PER_CPU(struct cpu_usage, cpu_usage_array);



extern void secondary_cpu_time_init(void);

extern void __init time_init(void);

arch/powerpc/kernel/process.c

+0 −14
Original line number Diff line number Diff line
@@ -846,10 +846,6 @@ bool ppc_breakpoint_available(void) 
}

EXPORT_SYMBOL_GPL(ppc_breakpoint_available);



#ifdef CONFIG_PPC64

DEFINE_PER_CPU(struct cpu_usage, cpu_usage_array);

#endif



static inline bool hw_brk_match(struct arch_hw_breakpoint *a,

			      struct arch_hw_breakpoint *b)

{
@@ -1182,16 +1178,6 @@ struct task_struct *__switch_to(struct task_struct *prev, 


	WARN_ON(!irqs_disabled());



#ifdef CONFIG_PPC64

	/*

	 * Collect processor utilization data per process

	 */

	if (firmware_has_feature(FW_FEATURE_SPLPAR)) {

		struct cpu_usage *cu = this_cpu_ptr(&cpu_usage_array);

		cu->current_tb = mfspr(SPRN_PURR);

	}

#endif /* CONFIG_PPC64 */



#ifdef CONFIG_PPC_BOOK3S_64

	batch = this_cpu_ptr(&ppc64_tlb_batch);

	if (batch->active) {

arch/powerpc/kernel/time.c

+0 −8
Original line number Diff line number Diff line
@@ -597,14 +597,6 @@ static void __timer_interrupt(void) 
		__this_cpu_inc(irq_stat.timer_irqs_others);

	}



#ifdef CONFIG_PPC64

	/* collect purr register values often, for accurate calculations */

	if (firmware_has_feature(FW_FEATURE_SPLPAR)) {

		struct cpu_usage *cu = this_cpu_ptr(&cpu_usage_array);

		cu->current_tb = mfspr(SPRN_PURR);

	}

#endif



	trace_timer_interrupt_exit(regs);

}

arch/powerpc/platforms/pseries/lparcfg.c

+10 −8
Original line number Diff line number Diff line
@@ -52,18 +52,20 @@ 
 * Track sum of all purrs across all processors. This is used to further

 * calculate usage values by different applications

 */

static void cpu_get_purr(void *arg)

{

	atomic64_t *sum = arg;



	atomic64_add(mfspr(SPRN_PURR), sum);

}



static unsigned long get_purr(void)

{

	unsigned long sum_purr = 0;

	int cpu;

	atomic64_t purr = ATOMIC64_INIT(0);



	for_each_possible_cpu(cpu) {

		struct cpu_usage *cu;

	on_each_cpu(cpu_get_purr, &purr, 1);



		cu = &per_cpu(cpu_usage_array, cpu);

		sum_purr += cu->current_tb;

	}

	return sum_purr;

	return atomic64_read(&purr);

}



/*