Bug 2390 - x86/paravirt: useless assignment instructions cause Unixbench full core performance degradation
Summary: x86/paravirt: useless assignment instructions cause Unixbench full core perfo...
Status: NEW
Alias: None
Product: ANCK 4.19 Dev
Classification: ANCK
Component: X86 (show other bugs) X86
Version: unspecified
Hardware: x86_64 Linux
: P3-Medium S5-enhancement
Target Milestone: ---
Assignee: Artie Ding
QA Contact: shuming
URL:
Whiteboard:
Keywords:
Depends on:
Blocks:
 
Reported: 2022-10-14 15:04 UTC by guohui
Modified: 2022-10-19 11:33 UTC (History)
2 users (show)

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Description guohui uniontech_group 2022-10-14 15:04:45 UTC 
Description of problem:
The instructions assigned to the vcpu_is_preempted function parameter
in the X86 architecture physical machine are redundant instructions, when config CONFIG_PARAVIRT_SPINLOCKS is turn on,
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

Version-Release number of selected component (if applicable):


How reproducible:


Steps to Reproduce:
1. Enter the Unixbench directory
2. ./Run -c 128 // 128 is the number of X86 physical machine cores
3. After removing the above command, run it again: ./Run -c 128

Actual results:
The score in step 3 is 400 to 500 more points than the score in step 2

Expected results:
Steps 2 and 3 have similar scores

Additional info:
N/A
Comment 1 guohui uniontech_group 2022-10-19 11:33:22 UTC 
Description of problem:
The instructions assigned to the vcpu_is_preempted function parameter
in the X86 architecture physical machine are redundant instructions, when config CONFIG_PARAVIRT_SPINLOCKS is turn on,
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: 4.19.90

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: 4.19.90

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

Version-Release number of selected component (if applicable):


How reproducible:


Steps to Reproduce:
in physical machine and config CONFIG_PARAVIRT_SPINLOCKS is turn on
1. Enter the Unixbench directory
2. ./Run -c 128 // 128 is the number of X86 physical machine cores
3. After removing the above command, run it again: ./Run -c 128

Actual results:
The score in step 3 is 400 to 500 more points than the score in step 2

Expected results:
Steps 2 and 3 have similar scores

Additional info:
N/A