From: "Gautham R. Shenoy" <e...@linux.vnet.ibm.com>
This patch exposes those extended CEDE states to the cpuidle framework
which are responsive to external interrupts and do not need an H_PROD.
Since as per the PAPR, all the extended CEDE states are non-responsive
to timers, we indicate this to the cpuidle subsystem via the
CPUIDLE_FLAG_TIMER_STOP flag for all those extende CEDE states which
can wake up on external interrupts.
With the patch, we are able to see the extended CEDE state with
latency hint = 1 exposed via the cpuidle framework.
$ cpupower idle-info
CPUidle driver: pseries_idle
CPUidle governor: menu
analyzing CPU 0:
Number of idle states: 3
Available idle states: snooze CEDE XCEDE1
snooze:
Flags/Description: snooze
Latency: 0
Usage: 33429446
Duration: 27006062
CEDE:
Flags/Description: CEDE
Latency: 1
Usage: 10272
Duration: 110786770
XCEDE1:
Flags/Description: XCEDE1
Latency: 12
Usage: 26445
Duration: 1436433815
Benchmark results:
TLDR: Over all we do not see any additional benefit from having XCEDE1 over
CEDE.
ebizzy :
2 threads bound to a big-core. With this patch, we see a 3.39%
regression compared to with only CEDE0 latency fixup.
x With only CEDE0 latency fixup
* With CEDE0 latency fixup + CEDE1
N Min Max Median Avg Stddev
x 10 2893813 5834474 5832448 5327281.3 1055941.4
* 10 2907329 5834923 5831398 5146614.6 1193874.8
context_switch2:
With the context_switch2 there are no observable regressions in the
results.
context_switch2 CPU0 CPU1 (Same Big-core, different small-cores).
No difference with and without patch.
x without_patch
* with_patch
N Min Max Median Avg Stddev
x 500 343644 348778 345444 345584.02 1035.1658
* 500 344310 347646 345776 345877.22 802.19501
context_switch2 CPU0 CPU8 (different big-cores). Minor 0.05% improvement
with patch
x without_patch
* with_patch
N Min Max Median Avg Stddev
x 500 287562 288756 288162 288134.76 262.24328
* 500 287874 288960 288306 288274.66 187.57034
schbench:
No regressions observed with schbench
Without Patch:
Latency percentiles (usec)
50.0th: 29
75.0th: 40
90.0th: 50
95.0th: 61
*99.0th: 13648
99.5th: 14768
99.9th: 15664
min=0, max=29812
With Patch:
Latency percentiles (usec)
50.0th: 30
75.0th: 40
90.0th: 51
95.0th: 59
*99.0th: 13616
99.5th: 14512
99.9th: 15696
min=0, max=15996
Signed-off-by: Gautham R. Shenoy <e...@linux.vnet.ibm.com>
---
drivers/cpuidle/cpuidle-pseries.c | 50 +++++++++++++++++++++++++++++++++++++++
1 file changed, 50 insertions(+)
diff --git a/drivers/cpuidle/cpuidle-pseries.c
b/drivers/cpuidle/cpuidle-pseries.c
index 502f906..6f893cd 100644
--- a/drivers/cpuidle/cpuidle-pseries.c
+++ b/drivers/cpuidle/cpuidle-pseries.c
@@ -362,9 +362,59 @@ static int add_pseries_idle_states(void)
for (i = 0; i < nr_xcede_records; i++) {
u64 latency_tb = xcede_records[i].wakeup_latency_tb_ticks;
u64 latency_us = tb_to_ns(latency_tb) / NSEC_PER_USEC;
+ char name[CPUIDLE_NAME_LEN];
+ unsigned int latency_hint = xcede_records[i].latency_hint;
+ u64 residency_us;
+
+ if (!xcede_records[i].responsive_to_irqs) {
+ pr_info("cpuidle : Skipping XCEDE%d. Not responsive to
IRQs\n",
+ latency_hint);
+ continue;
+ }
if (latency_us < min_latency_us)
min_latency_us = latency_us;
+ snprintf(name, CPUIDLE_NAME_LEN, "XCEDE%d", latency_hint);
+
+ /*
+ * As per the section 14.14.1 of PAPR version 2.8.1
+ * says that alling H_CEDE with the value of the cede
+ * latency specifier set greater than zero allows the
+ * processor timer facility to be disabled (so as not
+ * to cause gratuitous wake-ups - the use of H_PROD,
+ * or other external interrupt is required to wake the
+ * processor in this case).
+ *
+ * So, inform the cpuidle-subsystem that the timer
+ * will be stopped for these states.
+ *
+ * Also, bump up the latency by 10us, since cpuidle
+ * would use timer-offload framework which will need
+ * to send an IPI to wakeup a CPU whose timer has
+ * expired.
+ */
+ if (latency_hint > 0) {
+ dedicated_states[nr_states].flags =
CPUIDLE_FLAG_TIMER_STOP;
+ latency_us += 10;
+ }
+
+ /*
+ * Thumb rule : Reside in the XCEDE state for at least
+ * 10x the time required to enter and exit that state.
+ */
+ residency_us = latency_us * 10;
+
+ strlcpy(dedicated_states[nr_states].name, (const char *)name,
+ CPUIDLE_NAME_LEN);
+ strlcpy(dedicated_states[nr_states].desc, (const char *)name,
+ CPUIDLE_NAME_LEN);
+ dedicated_states[nr_states].exit_latency = latency_us;
+ dedicated_states[nr_states].target_residency = residency_us;
+ dedicated_states[nr_states].enter = &dedicated_cede_loop;
+ cede_latency_hint[nr_states] = latency_hint;
+ pr_info("cpuidle : Added %s. latency-hint = %d\n",
+ name, latency_hint);
+ nr_states++;
}
/*
--
1.9.4
