From ca3f969dcb111d35674b66bdcb72beb2c426b9b5 Mon Sep 17 00:00:00 2001
From: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Date: Wed, 2 Dec 2020 10:34:56 +0530
Subject: [PATCH] powerpc/paravirt: Use is_kvm_guest() in vcpu_is_preempted()
References: bsc#1181148 ltc#190702
Patch-mainline: v5.11-rc1
Git-commit: ca3f969dcb111d35674b66bdcb72beb2c426b9b5
If its a shared LPAR but not a KVM guest, then see if the vCPU is
related to the calling vCPU. On PowerVM, only cores can be preempted.
So if one vCPU is a non-preempted state, we can decipher that all
other vCPUs sharing the same core are in non-preempted state.
Performance results:
$ perf stat -r 5 -a perf bench sched pipe -l 10000000 (lesser time is better)
powerpc/next
35,107,951.20 msec cpu-clock # 255.898 CPUs utilized ( +- 0.31% )
23,655,348 context-switches # 0.674 K/sec ( +- 3.72% )
14,465 cpu-migrations # 0.000 K/sec ( +- 5.37% )
82,463 page-faults # 0.002 K/sec ( +- 8.40% )
1,127,182,328,206 cycles # 0.032 GHz ( +- 1.60% ) (66.67%)
78,587,300,622 stalled-cycles-frontend # 6.97% frontend cycles idle ( +- 0.08% ) (50.01%)
654,124,218,432 stalled-cycles-backend # 58.03% backend cycles idle ( +- 1.74% ) (50.01%)
834,013,059,242 instructions # 0.74 insn per cycle
# 0.78 stalled cycles per insn ( +- 0.73% ) (66.67%)
132,911,454,387 branches # 3.786 M/sec ( +- 0.59% ) (50.00%)
2,890,882,143 branch-misses # 2.18% of all branches ( +- 0.46% ) (50.00%)
137.195 +- 0.419 seconds time elapsed ( +- 0.31% )
powerpc/next + patchset
29,981,702.64 msec cpu-clock # 255.881 CPUs utilized ( +- 1.30% )
40,162,456 context-switches # 0.001 M/sec ( +- 0.01% )
1,110 cpu-migrations # 0.000 K/sec ( +- 5.20% )
62,616 page-faults # 0.002 K/sec ( +- 3.93% )
1,430,030,626,037 cycles # 0.048 GHz ( +- 1.41% ) (66.67%)
83,202,707,288 stalled-cycles-frontend # 5.82% frontend cycles idle ( +- 0.75% ) (50.01%)
744,556,088,520 stalled-cycles-backend # 52.07% backend cycles idle ( +- 1.39% ) (50.01%)
940,138,418,674 instructions # 0.66 insn per cycle
# 0.79 stalled cycles per insn ( +- 0.51% ) (66.67%)
146,452,852,283 branches # 4.885 M/sec ( +- 0.80% ) (50.00%)
3,237,743,996 branch-misses # 2.21% of all branches ( +- 1.18% ) (50.01%)
117.17 +- 1.52 seconds time elapsed ( +- 1.30% )
This is around 14.6% improvement in performance.
Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Acked-by: Waiman Long <longman@redhat.com>
[mpe: Fold in performance results from cover letter]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201202050456.164005-5-srikar@linux.vnet.ibm.com
Acked-by: Michal Suchanek <msuchanek@suse.de>
---
arch/powerpc/include/asm/paravirt.h | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
diff --git a/arch/powerpc/include/asm/paravirt.h b/arch/powerpc/include/asm/paravirt.h
index 9362c94fe3aa..edc08f04aef7 100644
--- a/arch/powerpc/include/asm/paravirt.h
+++ b/arch/powerpc/include/asm/paravirt.h
@@ -10,6 +10,9 @@
#endif
#ifdef CONFIG_PPC_SPLPAR
+#include <asm/kvm_guest.h>
+#include <asm/cputhreads.h>
+
DECLARE_STATIC_KEY_FALSE(shared_processor);
static inline bool is_shared_processor(void)
@@ -74,6 +77,21 @@ static inline bool vcpu_is_preempted(int cpu)
{
if (!is_shared_processor())
return false;
+
+#ifdef CONFIG_PPC_SPLPAR
+ if (!is_kvm_guest()) {
+ int first_cpu = cpu_first_thread_sibling(smp_processor_id());
+
+ /*
+ * Preemption can only happen at core granularity. This CPU
+ * is not preempted if one of the CPU of this core is not
+ * preempted.
+ */
+ if (cpu_first_thread_sibling(cpu) == first_cpu)
+ return false;
+ }
+#endif
+
if (yield_count_of(cpu) & 1)
return true;
return false;
--
2.31.1