From: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com>
To: Nicholas Piggin <npiggin@gmail.com>,
Anton Blanchard <anton@ozlabs.org>,
Nathan Lynch <nathanl@linux.ibm.com>,
Michael Ellerman <mpe@ellerman.id.au>,
Michael Neuling <mikey@neuling.org>,
Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Cc: linuxppc-dev@ozlabs.org, linux-kernel@vger.kernel.org,
linux-pm@vger.kernel.org,
"Gautham R. Shenoy" <ego@linux.vnet.ibm.com>
Subject: [PATCH v2 3/3] cpuidle-pseries : Fixup exit latency for CEDE(0)
Date: Wed, 29 Jul 2020 12:17:34 +0530 [thread overview]
Message-ID: <1596005254-25753-4-git-send-email-ego@linux.vnet.ibm.com> (raw)
In-Reply-To: <1596005254-25753-1-git-send-email-ego@linux.vnet.ibm.com>
From: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com>
We are currently assuming that CEDE(0) has exit latency 10us, since
there is no way for us to query from the platform. However, if the
wakeup latency of an Extended CEDE state is smaller than 10us, then we
can be sure that the exit latency of CEDE(0) cannot be more than that.
that.
In this patch, we fix the exit latency of CEDE(0) if we discover an
Extended CEDE state with wakeup latency smaller than 10us.
Benchmark results:
ebizzy:
2 ebizzy threads bound to the same big-core. 25% improvement in the
avg records/s with patch.
x without_patch
+ with_patch
N Min Max Median Avg Stddev
x 10 2491089 5834307 5398375 4244335 1596244.9
+ 10 2893813 5834474 5832448 5327281.3 1055941.4
context_switch2 :
There is no major regression observed with this patch as seen from the
context_switch2 benchmark.
context_switch2 across CPU0 CPU1 (Both belong to same big-core, but different
small cores). We observe a minor 0.14% regression in the number of
context-switches (higher is better).
x without_patch
+ with_patch
N Min Max Median Avg Stddev
x 500 348872 362236 354712 354745.69 2711.827
+ 500 349422 361452 353942 354215.4 2576.9258
Difference at 99.0% confidence
-530.288 +/- 430.963
-0.149484% +/- 0.121485%
(Student's t, pooled s = 2645.24)
context_switch2 across CPU0 CPU8 (Different big-cores). We observe a 0.37%
improvement in the number of context-switches (higher is better).
x without_patch
+ with_patch
N Min Max Median Avg Stddev
x 500 287956 294940 288896 288977.23 646.59295
+ 500 288300 294646 289582 290064.76 1161.9992
Difference at 99.0% confidence
1087.53 +/- 153.194
0.376337% +/- 0.0530125%
(Student's t, pooled s = 940.299)
schbench:
No major difference could be seen until the 99.9th percentile.
Without-patch
Latency percentiles (usec)
50.0th: 29
75.0th: 39
90.0th: 49
95.0th: 59
*99.0th: 13104
99.5th: 14672
99.9th: 15824
min=0, max=17993
With-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
Reviewed-by: Vaidyanathan Srinivasan <svaidy@linux.ibm.com>
Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
---
drivers/cpuidle/cpuidle-pseries.c | 34 ++++++++++++++++++++++++++++++++--
1 file changed, 32 insertions(+), 2 deletions(-)
diff --git a/drivers/cpuidle/cpuidle-pseries.c b/drivers/cpuidle/cpuidle-pseries.c
index b1dc24d..0b2f115 100644
--- a/drivers/cpuidle/cpuidle-pseries.c
+++ b/drivers/cpuidle/cpuidle-pseries.c
@@ -334,12 +334,42 @@ static int pseries_cpuidle_driver_init(void)
static int add_pseries_idle_states(void)
{
int nr_states = 2; /* By default we have snooze, CEDE */
+ int i;
+ u64 min_latency_us = dedicated_states[1].exit_latency; /* CEDE latency */
if (parse_cede_parameters())
return nr_states;
- pr_info("cpuidle : Skipping the %d Extended CEDE idle states\n",
- nr_xcede_records);
+ 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;
+
+ if (latency_us < min_latency_us)
+ min_latency_us = latency_us;
+ }
+
+ /*
+ * We are currently assuming that CEDE(0) has exit latency
+ * 10us, since there is no way for us to query from the
+ * platform.
+ *
+ * However, if the wakeup latency of an Extended CEDE state is
+ * smaller than 10us, then we can be sure that CEDE(0)
+ * requires no more than that.
+ *
+ * Perform the fix-up.
+ */
+ if (min_latency_us < dedicated_states[1].exit_latency) {
+ u64 cede0_latency = min_latency_us - 1;
+
+ if (cede0_latency <= 0)
+ cede0_latency = min_latency_us;
+
+ dedicated_states[1].exit_latency = cede0_latency;
+ dedicated_states[1].target_residency = 10 * (cede0_latency);
+ pr_info("cpuidle : Fixed up CEDE exit latency to %llu us\n",
+ cede0_latency);
+ }
return nr_states;
}
--
1.9.4
prev parent reply other threads:[~2020-07-29 6:48 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-29 6:47 [PATCH v2 0/3] cpuidle-pseries: Parse extended CEDE information for idle Gautham R. Shenoy
2020-07-29 6:47 ` [PATCH v2 1/3] cpuidle-pseries: Set the latency-hint before entering CEDE Gautham R. Shenoy
2020-07-29 6:47 ` [PATCH v2 2/3] cpuidle-pseries: Add function to parse extended CEDE records Gautham R. Shenoy
2020-07-29 6:47 ` Gautham R. Shenoy [this message]
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