Avoid reading node->prev in vcpu_is_preempted in osq_lock to reduce cache miss for bare-metal environment.
Guo Hui (1): x86/paravirt: useless assignment instructions cause Unixbench full core performance degradation
Zheng Zengkai (1): arm64/paravirt: disable vcpu_has_preemption if PV sched can't be used
arch/arm64/kernel/paravirt.c | 3 +++ arch/x86/kernel/paravirt-spinlocks.c | 4 ++++ kernel/locking/osq_lock.c | 19 ++++++++++++++++++- 3 files changed, 25 insertions(+), 1 deletion(-)
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From: Guo Hui guohui@uniontech.com
maillist inclusion category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I9IRPK Reference: https://lore.kernel.org/lkml/20220628161251.21950-1-guohui@uniontech.com/
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The instructions assigned to the vcpu_is_preempted function parameter in the X86 architecture physical machine are redundant instructions, causing the multi-core performance of Unixbench to drop by about 4% to 5%. The C function is as follows: static bool vcpu_is_preempted(long vcpu);
The parameter 'vcpu' in the function osq_lock that calls the function vcpu_is_preempted is assigned as follows:
The C code is in the function node_cpu: cpu = node->cpu - 1;
The instructions corresponding to the C code are: mov 0x14(%rax),%edi sub $0x1,%edi
The above instructions are unnecessary in the X86 Native operating environment, causing high cache-misses and degrading performance.
This patch uses static_key to not execute this instruction in the Native runtime environment.
The patch effect is as follows two machines, Unixbench runs with full core score:
1. Machine configuration: Intel(R) Xeon(R) Silver 4210 CPU @ 2.20GHz CPU core: 40 Memory: 256G OS Kernel: 5.19-rc3
Before using the patch: System Benchmarks Index Values BASELINE RESULT INDEX Dhrystone 2 using register variables 116700.0 948326591.2 81261.9 Double-Precision Whetstone 55.0 211986.3 38543.0 Execl Throughput 43.0 43453.2 10105.4 File Copy 1024 bufsize 2000 maxblocks 3960.0 438936.2 1108.4 File Copy 256 bufsize 500 maxblocks 1655.0 118197.4 714.2 File Copy 4096 bufsize 8000 maxblocks 5800.0 1534674.7 2646.0 Pipe Throughput 12440.0 46482107.6 37365.0 Pipe-based Context Switching 4000.0 1915094.2 4787.7 Process Creation 126.0 85442.2 6781.1 Shell Scripts (1 concurrent) 42.4 69400.7 16368.1 Shell Scripts (8 concurrent) 6.0 8877.2 14795.3 System Call Overhead 15000.0 4714906.1 3143.3 ======== System Benchmarks Index Score 7923.3
After using the patch: System Benchmarks Index Values BASELINE RESULT INDEX Dhrystone 2 using register variables 116700.0 947032915.5 81151.1 Double-Precision Whetstone 55.0 211971.2 38540.2 Execl Throughput 43.0 45054.8 10477.9 File Copy 1024 bufsize 2000 maxblocks 3960.0 515024.9 1300.6 File Copy 256 bufsize 500 maxblocks 1655.0 146354.6 884.3 File Copy 4096 bufsize 8000 maxblocks 5800.0 1679995.9 2896.5 Pipe Throughput 12440.0 46466394.2 37352.4 Pipe-based Context Switching 4000.0 1898221.4 4745.6 Process Creation 126.0 85653.1 6797.9 Shell Scripts (1 concurrent) 42.4 69437.3 16376.7 Shell Scripts (8 concurrent) 6.0 8898.9 14831.4 System Call Overhead 15000.0 4658746.7 3105.8 ======== System Benchmarks Index Score 8248.8
2. Machine configuration: Hygon C86 7185 32-core Processor CPU core: 128 Memory: 256G OS Kernel: 5.19-rc3
Before using the patch: System Benchmarks Index Values BASELINE RESULT INDEX Dhrystone 2 using register variables 116700.0 2256644068.3 193371.4 Double-Precision Whetstone 55.0 438969.9 79812.7 Execl Throughput 43.0 10108.6 2350.8 File Copy 1024 bufsize 2000 maxblocks 3960.0 275892.8 696.7 File Copy 256 bufsize 500 maxblocks 1655.0 72082.7 435.5 File Copy 4096 bufsize 8000 maxblocks 5800.0 925043.4 1594.9 Pipe Throughput 12440.0 118905512.5 95583.2 Pipe-based Context Switching 4000.0 7820945.7 19552.4 Process Creation 126.0 31233.3 2478.8 Shell Scripts (1 concurrent) 42.4 49042.8 11566.7 Shell Scripts (8 concurrent) 6.0 6656.0 11093.3 System Call Overhead 15000.0 6816047.5 4544.0 ======== System Benchmarks Index Score 7756.6
After using the patch: System Benchmarks Index Values BASELINE RESULT INDEX Dhrystone 2 using register variables 116700.0 2252272929.4 192996.8 Double-Precision Whetstone 55.0 451847.2 82154.0 Execl Throughput 43.0 10595.1 2464.0 File Copy 1024 bufsize 2000 maxblocks 3960.0 301279.3 760.8 File Copy 256 bufsize 500 maxblocks 1655.0 79291.3 479.1 File Copy 4096 bufsize 8000 maxblocks 5800.0 1039755.2 1792.7 Pipe Throughput 12440.0 118701468.1 95419.2 Pipe-based Context Switching 4000.0 8073453.3 20183.6 Process Creation 126.0 33440.9 2654.0 Shell Scripts (1 concurrent) 42.4 52722.6 12434.6 Shell Scripts (8 concurrent) 6.0 7050.4 11750.6 System Call Overhead 15000.0 6834371.5 4556.2 ======== System Benchmarks Index Score 8157.8
Signed-off-by: Guo Hui guohui@uniontech.com Signed-off-by: Zheng Zengkai zhengzengkai@huawei.com --- arch/x86/kernel/paravirt-spinlocks.c | 4 ++++ kernel/locking/osq_lock.c | 19 ++++++++++++++++++- 2 files changed, 22 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kernel/paravirt-spinlocks.c b/arch/x86/kernel/paravirt-spinlocks.c index 9e1ea99ad9df..a2eb375e21e3 100644 --- a/arch/x86/kernel/paravirt-spinlocks.c +++ b/arch/x86/kernel/paravirt-spinlocks.c @@ -33,6 +33,8 @@ bool pv_is_native_vcpu_is_preempted(void) __raw_callee_save___native_vcpu_is_preempted; }
+DECLARE_STATIC_KEY_TRUE(vcpu_has_preemption); + void __init paravirt_set_cap(void) { if (!pv_is_native_spin_unlock()) @@ -40,4 +42,6 @@ void __init paravirt_set_cap(void)
if (!pv_is_native_vcpu_is_preempted()) setup_force_cpu_cap(X86_FEATURE_VCPUPREEMPT); + else + static_branch_disable(&vcpu_has_preemption); } diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c index 17618d62343f..7513d6f3cf48 100644 --- a/kernel/locking/osq_lock.c +++ b/kernel/locking/osq_lock.c @@ -27,6 +27,23 @@ static inline int node_cpu(struct optimistic_spin_node *node) return node->cpu - 1; }
+#ifdef vcpu_is_preempted +DEFINE_STATIC_KEY_TRUE(vcpu_has_preemption); + +static inline bool vcpu_is_preempted_node(struct optimistic_spin_node *node) +{ + if (static_branch_likely(&vcpu_has_preemption)) + return vcpu_is_preempted(node_cpu(node->prev)); + + return false; +} +#else +static inline bool vcpu_is_preempted_node(struct optimistic_spin_node *node) +{ + return false; +} +#endif + static inline struct optimistic_spin_node *decode_cpu(int encoded_cpu_val) { int cpu_nr = encoded_cpu_val - 1; @@ -147,7 +164,7 @@ bool osq_lock(struct optimistic_spin_queue *lock) * polling, be careful. */ if (smp_cond_load_relaxed(&node->locked, VAL || need_resched() || - vcpu_is_preempted(node_cpu(node->prev)))) + vcpu_is_preempted_node(node))) return true;
/* unqueue */
hulk inclusion category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I9IRPK
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For arm64 physical machine, vcpu_is_preempted() is also redundant, disable vcpu_has_preemption static key if PV sched can't be used to reduce cache-misses influence.
Signed-off-by: Zheng Zengkai zhengzengkai@huawei.com --- arch/arm64/kernel/paravirt.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/arch/arm64/kernel/paravirt.c b/arch/arm64/kernel/paravirt.c index 53bb6fa76366..e66dd05a849d 100644 --- a/arch/arm64/kernel/paravirt.c +++ b/arch/arm64/kernel/paravirt.c @@ -259,6 +259,8 @@ static bool has_kvm_pvsched(void) return (res.a0 == SMCCC_RET_SUCCESS); }
+DECLARE_STATIC_KEY_TRUE(vcpu_has_preemption); + int __init pv_sched_init(void) { int ret; @@ -276,6 +278,7 @@ int __init pv_sched_init(void) return ret;
static_call_update(pv_vcpu_preempted, kvm_vcpu_is_preempted); + static_branch_disable(&vcpu_has_preemption); pr_info("using PV sched preempted\n");
return 0;
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Zheng Zengkai