[PATCH 0/4] Powerpc: Better preemption for shared processor

[PATCH 0/4] Powerpc: Better preemption for shared processor

[Srikar Dronamraju]

Currently, vcpu_is_preempted will return the yield_count for
shared_processor. On a PowerVM LPAR, Phyp schedules at SMT8 core boundary
i.e all CPUs belonging to a core are either group scheduled in or group
scheduled out. This can be used to better predict non-preempted CPUs on
PowerVM shared LPARs.

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.

Cc: linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
Cc: LKML <linux-kernel@vger.kernel.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Nathan Lynch <nathanl@linux.ibm.com>
Cc: Gautham R Shenoy <ego@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Valentin Schneider <valentin.schneider@arm.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Waiman Long <longman@redhat.com>
Cc: Phil Auld <pauld@redhat.com>

Srikar Dronamraju (4):
  powerpc: Refactor is_kvm_guest declaration to new header
  powerpc: Rename is_kvm_guest to check_kvm_guest
  powerpc: Reintroduce is_kvm_guest
  powerpc/paravirt: Use is_kvm_guest in vcpu_is_preempted

 arch/powerpc/include/asm/firmware.h  |  6 ------
 arch/powerpc/include/asm/kvm_guest.h | 25 +++++++++++++++++++++++++
 arch/powerpc/include/asm/kvm_para.h  |  2 +-
 arch/powerpc/include/asm/paravirt.h  | 18 ++++++++++++++++++
 arch/powerpc/kernel/firmware.c       |  5 ++++-
 arch/powerpc/platforms/pseries/smp.c |  3 ++-
 6 files changed, 50 insertions(+), 9 deletions(-)
 create mode 100644 arch/powerpc/include/asm/kvm_guest.h

-- 
2.18.4

[PATCH 1/4] powerpc: Refactor is_kvm_guest declaration to new header

[Srikar Dronamraju]

Only code/declaration movement, in anticipation of doing a kvm-aware
vcpu_is_preempted. No additional changes.

Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
Cc: LKML <linux-kernel@vger.kernel.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Nathan Lynch <nathanl@linux.ibm.com>
Cc: Gautham R Shenoy <ego@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Valentin Schneider <valentin.schneider@arm.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Waiman Long <longman@redhat.com>
Cc: Phil Auld <pauld@redhat.com>
---
 arch/powerpc/include/asm/firmware.h  |  6 ------
 arch/powerpc/include/asm/kvm_guest.h | 15 +++++++++++++++
 arch/powerpc/include/asm/kvm_para.h  |  2 +-
 arch/powerpc/platforms/pseries/smp.c |  1 +
 4 files changed, 17 insertions(+), 7 deletions(-)
 create mode 100644 arch/powerpc/include/asm/kvm_guest.h

diff --git a/arch/powerpc/include/asm/firmware.h b/arch/powerpc/include/asm/firmware.h
index 0b295bdb201e..aa6a5ef5d483 100644
--- a/arch/powerpc/include/asm/firmware.h
+++ b/arch/powerpc/include/asm/firmware.h
@@ -134,12 +134,6 @@ extern int ibm_nmi_interlock_token;
 
 extern unsigned int __start___fw_ftr_fixup, __stop___fw_ftr_fixup;
 
-#if defined(CONFIG_PPC_PSERIES) || defined(CONFIG_KVM_GUEST)
-bool is_kvm_guest(void);
-#else
-static inline bool is_kvm_guest(void) { return false; }
-#endif
-
 #ifdef CONFIG_PPC_PSERIES
 void pseries_probe_fw_features(void);
 #else
diff --git a/arch/powerpc/include/asm/kvm_guest.h b/arch/powerpc/include/asm/kvm_guest.h
new file mode 100644
index 000000000000..c0ace884a0e8
--- /dev/null
+++ b/arch/powerpc/include/asm/kvm_guest.h
@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2020  IBM Corporation
+ */
+
+#ifndef __POWERPC_KVM_GUEST_H__
+#define __POWERPC_KVM_GUEST_H__
+
+#if defined(CONFIG_PPC_PSERIES) || defined(CONFIG_KVM_GUEST)
+bool is_kvm_guest(void);
+#else
+static inline bool is_kvm_guest(void) { return false; }
+#endif
+
+#endif /* __POWERPC_KVM_GUEST_H__ */
diff --git a/arch/powerpc/include/asm/kvm_para.h b/arch/powerpc/include/asm/kvm_para.h
index 744612054c94..abe1b5e82547 100644
--- a/arch/powerpc/include/asm/kvm_para.h
+++ b/arch/powerpc/include/asm/kvm_para.h
@@ -8,7 +8,7 @@
 #ifndef __POWERPC_KVM_PARA_H__
 #define __POWERPC_KVM_PARA_H__
 
-#include <asm/firmware.h>
+#include <asm/kvm_guest.h>
 
 #include <uapi/asm/kvm_para.h>
 
diff --git a/arch/powerpc/platforms/pseries/smp.c b/arch/powerpc/platforms/pseries/smp.c
index 92922491a81c..d578732c545d 100644
--- a/arch/powerpc/platforms/pseries/smp.c
+++ b/arch/powerpc/platforms/pseries/smp.c
@@ -42,6 +42,7 @@
 #include <asm/plpar_wrappers.h>
 #include <asm/code-patching.h>
 #include <asm/svm.h>
+#include <asm/kvm_guest.h>
 
 #include "pseries.h"
 
-- 
2.18.4

[PATCH 2/4] powerpc: Rename is_kvm_guest to check_kvm_guest

[Srikar Dronamraju]

is_kvm_guest() will be reused in subsequent patch in a new avatar.  Hence
rename is_kvm_guest to check_kvm_guest. No additional changes.

Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
Cc: LKML <linux-kernel@vger.kernel.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Nathan Lynch <nathanl@linux.ibm.com>
Cc: Gautham R Shenoy <ego@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Valentin Schneider <valentin.schneider@arm.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Waiman Long <longman@redhat.com>
Cc: Phil Auld <pauld@redhat.com>
---
 arch/powerpc/include/asm/kvm_guest.h | 4 ++--
 arch/powerpc/include/asm/kvm_para.h  | 2 +-
 arch/powerpc/kernel/firmware.c       | 2 +-
 arch/powerpc/platforms/pseries/smp.c | 2 +-
 4 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/include/asm/kvm_guest.h b/arch/powerpc/include/asm/kvm_guest.h
index c0ace884a0e8..ba8291e02ba9 100644
--- a/arch/powerpc/include/asm/kvm_guest.h
+++ b/arch/powerpc/include/asm/kvm_guest.h
@@ -7,9 +7,9 @@
 #define __POWERPC_KVM_GUEST_H__
 
 #if defined(CONFIG_PPC_PSERIES) || defined(CONFIG_KVM_GUEST)
-bool is_kvm_guest(void);
+bool check_kvm_guest(void);
 #else
-static inline bool is_kvm_guest(void) { return false; }
+static inline bool check_kvm_guest(void) { return false; }
 #endif
 
 #endif /* __POWERPC_KVM_GUEST_H__ */
diff --git a/arch/powerpc/include/asm/kvm_para.h b/arch/powerpc/include/asm/kvm_para.h
index abe1b5e82547..6fba06b6cfdb 100644
--- a/arch/powerpc/include/asm/kvm_para.h
+++ b/arch/powerpc/include/asm/kvm_para.h
@@ -14,7 +14,7 @@
 
 static inline int kvm_para_available(void)
 {
-	return IS_ENABLED(CONFIG_KVM_GUEST) && is_kvm_guest();
+	return IS_ENABLED(CONFIG_KVM_GUEST) && check_kvm_guest();
 }
 
 static inline unsigned int kvm_arch_para_features(void)
diff --git a/arch/powerpc/kernel/firmware.c b/arch/powerpc/kernel/firmware.c
index fe48d319d490..61243267d4cf 100644
--- a/arch/powerpc/kernel/firmware.c
+++ b/arch/powerpc/kernel/firmware.c
@@ -21,7 +21,7 @@ EXPORT_SYMBOL_GPL(powerpc_firmware_features);
 #endif
 
 #if defined(CONFIG_PPC_PSERIES) || defined(CONFIG_KVM_GUEST)
-bool is_kvm_guest(void)
+bool check_kvm_guest(void)
 {
 	struct device_node *hyper_node;
 
diff --git a/arch/powerpc/platforms/pseries/smp.c b/arch/powerpc/platforms/pseries/smp.c
index d578732c545d..c70b4be9f0a5 100644
--- a/arch/powerpc/platforms/pseries/smp.c
+++ b/arch/powerpc/platforms/pseries/smp.c
@@ -211,7 +211,7 @@ static __init void pSeries_smp_probe(void)
 	if (!cpu_has_feature(CPU_FTR_SMT))
 		return;
 
-	if (is_kvm_guest()) {
+	if (check_kvm_guest()) {
 		/*
 		 * KVM emulates doorbells by disabling FSCR[MSGP] so msgsndp
 		 * faults to the hypervisor which then reads the instruction
-- 
2.18.4

[PATCH 3/4] powerpc: Reintroduce is_kvm_guest in a new avatar

[Srikar Dronamraju]

Introduce a static branch that would be set during boot if the OS
happens to be a KVM guest. Subsequent checks to see if we are on KVM
will rely on this static branch. This static branch would be used in
vcpu_is_preempted in a subsequent patch.

Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
Cc: LKML <linux-kernel@vger.kernel.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Nathan Lynch <nathanl@linux.ibm.com>
Cc: Gautham R Shenoy <ego@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Valentin Schneider <valentin.schneider@arm.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Waiman Long <longman@redhat.com>
Cc: Phil Auld <pauld@redhat.com>
---
 arch/powerpc/include/asm/kvm_guest.h | 10 ++++++++++
 arch/powerpc/include/asm/kvm_para.h  |  2 +-
 arch/powerpc/kernel/firmware.c       |  3 +++
 3 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/kvm_guest.h b/arch/powerpc/include/asm/kvm_guest.h
index ba8291e02ba9..627ba272e781 100644
--- a/arch/powerpc/include/asm/kvm_guest.h
+++ b/arch/powerpc/include/asm/kvm_guest.h
@@ -7,8 +7,18 @@
 #define __POWERPC_KVM_GUEST_H__
 
 #if defined(CONFIG_PPC_PSERIES) || defined(CONFIG_KVM_GUEST)
+#include <linux/jump_label.h>
+
+DECLARE_STATIC_KEY_FALSE(kvm_guest);
+
+static inline bool is_kvm_guest(void)
+{
+	return static_branch_unlikely(&kvm_guest);
+}
+
 bool check_kvm_guest(void);
 #else
+static inline bool is_kvm_guest(void) { return false; }
 static inline bool check_kvm_guest(void) { return false; }
 #endif
 
diff --git a/arch/powerpc/include/asm/kvm_para.h b/arch/powerpc/include/asm/kvm_para.h
index 6fba06b6cfdb..abe1b5e82547 100644
--- a/arch/powerpc/include/asm/kvm_para.h
+++ b/arch/powerpc/include/asm/kvm_para.h
@@ -14,7 +14,7 @@
 
 static inline int kvm_para_available(void)
 {
-	return IS_ENABLED(CONFIG_KVM_GUEST) && check_kvm_guest();
+	return IS_ENABLED(CONFIG_KVM_GUEST) && is_kvm_guest();
 }
 
 static inline unsigned int kvm_arch_para_features(void)
diff --git a/arch/powerpc/kernel/firmware.c b/arch/powerpc/kernel/firmware.c
index 61243267d4cf..28498fc573f2 100644
--- a/arch/powerpc/kernel/firmware.c
+++ b/arch/powerpc/kernel/firmware.c
@@ -14,6 +14,7 @@
 #include <linux/of.h>
 
 #include <asm/firmware.h>
+#include <asm/kvm_guest.h>
 
 #ifdef CONFIG_PPC64
 unsigned long powerpc_firmware_features __read_mostly;
@@ -21,6 +22,7 @@ EXPORT_SYMBOL_GPL(powerpc_firmware_features);
 #endif
 
 #if defined(CONFIG_PPC_PSERIES) || defined(CONFIG_KVM_GUEST)
+DEFINE_STATIC_KEY_FALSE(kvm_guest);
 bool check_kvm_guest(void)
 {
 	struct device_node *hyper_node;
@@ -32,6 +34,7 @@ bool check_kvm_guest(void)
 	if (!of_device_is_compatible(hyper_node, "linux,kvm"))
 		return 0;
 
+	static_branch_enable(&kvm_guest);
 	return 1;
 }
 #endif
-- 
2.18.4

[PATCH 4/4] powerpc/paravirt: Use is_kvm_guest in vcpu_is_preempted

[Srikar Dronamraju]

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.

Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
Cc: LKML <linux-kernel@vger.kernel.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Nathan Lynch <nathanl@linux.ibm.com>
Cc: Gautham R Shenoy <ego@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Valentin Schneider <valentin.schneider@arm.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Waiman Long <longman@redhat.com>
Cc: Phil Auld <pauld@redhat.com>
---
 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;
-- 
2.18.4

Re: [PATCH 0/4] Powerpc: Better preemption for shared processor

[Waiman Long]

On 10/28/20 8:35 AM, Srikar Dronamraju wrote:
> Currently, vcpu_is_preempted will return the yield_count for
> shared_processor. On a PowerVM LPAR, Phyp schedules at SMT8 core boundary
> i.e all CPUs belonging to a core are either group scheduled in or group
> scheduled out. This can be used to better predict non-preempted CPUs on
> PowerVM shared LPARs.
>
> 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.
>
> Cc: linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
> Cc: LKML <linux-kernel@vger.kernel.org>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: Nicholas Piggin <npiggin@gmail.com>
> Cc: Nathan Lynch <nathanl@linux.ibm.com>
> Cc: Gautham R Shenoy <ego@linux.vnet.ibm.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Valentin Schneider <valentin.schneider@arm.com>
> Cc: Juri Lelli <juri.lelli@redhat.com>
> Cc: Waiman Long <longman@redhat.com>
> Cc: Phil Auld <pauld@redhat.com>
>
> Srikar Dronamraju (4):
>    powerpc: Refactor is_kvm_guest declaration to new header
>    powerpc: Rename is_kvm_guest to check_kvm_guest
>    powerpc: Reintroduce is_kvm_guest
>    powerpc/paravirt: Use is_kvm_guest in vcpu_is_preempted
>
>   arch/powerpc/include/asm/firmware.h  |  6 ------
>   arch/powerpc/include/asm/kvm_guest.h | 25 +++++++++++++++++++++++++
>   arch/powerpc/include/asm/kvm_para.h  |  2 +-
>   arch/powerpc/include/asm/paravirt.h  | 18 ++++++++++++++++++
>   arch/powerpc/kernel/firmware.c       |  5 ++++-
>   arch/powerpc/platforms/pseries/smp.c |  3 ++-
>   6 files changed, 50 insertions(+), 9 deletions(-)
>   create mode 100644 arch/powerpc/include/asm/kvm_guest.h
>
This patch series looks good to me and the performance is nice too.

Acked-by: Waiman Long <longman@redhat.com>

Just curious, is the performance mainly from the use of static_branch 
(patches 1 - 3) or from reducing call to yield_count_of().

Cheers,
Longman

Re: [PATCH 0/4] Powerpc: Better preemption for shared processor

[Srikar Dronamraju]

* Waiman Long <longman@redhat.com> [2020-10-28 20:01:30]:

> > Srikar Dronamraju (4):
> >    powerpc: Refactor is_kvm_guest declaration to new header
> >    powerpc: Rename is_kvm_guest to check_kvm_guest
> >    powerpc: Reintroduce is_kvm_guest
> >    powerpc/paravirt: Use is_kvm_guest in vcpu_is_preempted
> > 
> >   arch/powerpc/include/asm/firmware.h  |  6 ------
> >   arch/powerpc/include/asm/kvm_guest.h | 25 +++++++++++++++++++++++++
> >   arch/powerpc/include/asm/kvm_para.h  |  2 +-
> >   arch/powerpc/include/asm/paravirt.h  | 18 ++++++++++++++++++
> >   arch/powerpc/kernel/firmware.c       |  5 ++++-
> >   arch/powerpc/platforms/pseries/smp.c |  3 ++-
> >   6 files changed, 50 insertions(+), 9 deletions(-)
> >   create mode 100644 arch/powerpc/include/asm/kvm_guest.h
> > 
> This patch series looks good to me and the performance is nice too.
> 
> Acked-by: Waiman Long <longman@redhat.com>

Thank you.

> 
> Just curious, is the performance mainly from the use of static_branch
> (patches 1 - 3) or from reducing call to yield_count_of().

Because of the reduced call to yield_count

> 
> Cheers,
> Longman
> 

-- 
Thanks and Regards
Srikar Dronamraju