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powerpc/pseries: lparcfg calculate PURR on demand

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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: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Nicholas Piggin
2018-05-05 03:19:30 +10:00
committed by Michael Ellerman
parent 36d632ea83
commit 3d3a6021dd
4 changed files with 10 additions and 38 deletions
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18
arch/powerpc/platforms/pseries/lparcfg.c
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@@ -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);
}
/*