Linux kernel 为什么是cpu;每周期insn“;在类似的cpu中是不同的,如何;MONITOR-MWAIT“;在Linux中工作?
背景: 我有2台服务器,所有的操作系统内核版本都是4.18.7,它有CONFIG\u BPF\u SYSCALL=y 我创建了一个shell脚本“x.sh”Linux kernel 为什么是cpu;每周期insn“;在类似的cpu中是不同的,如何;MONITOR-MWAIT“;在Linux中工作?,linux-kernel,cpu,perf,branch-prediction,Linux Kernel,Cpu,Perf,Branch Prediction,背景: 我有2台服务器,所有的操作系统内核版本都是4.18.7,它有CONFIG\u BPF\u SYSCALL=y 我创建了一个shell脚本“x.sh” i=0 while (( i < 1000000 )) do (( i ++ )) done S2: CPU--Intel(R)Xeon(R)CPU E5-2620 v4@2.10GHz,微码--0xb00002e 和性能统计结果 5391.653531 task-clock (msec) #
i=0
while (( i < 1000000 ))
do (( i ++ ))
done
S2:
CPU--Intel(R)Xeon(R)CPU E5-2620 v4@2.10GHz,微码--0xb00002e
和性能统计结果
5391.653531 task-clock (msec) # 1.000 CPUs utilized
4 context-switches # 0.001 K/sec
0 cpu-migrations # 0.000 K/sec
107 page-faults # 0.020 K/sec
12,910,036,202 cycles # 2.394 GHz
27,055,073,385 instructions # 2.10 insn per cycle
6,527,267,657 branches # 1210.624 M/sec
34,787,686 branch-misses # 0.53% of all branches
5.392121575 seconds time elapsed
10688.669439 task-clock (msec) # 1.000 CPUs utilized
6 context-switches # 0.001 K/sec
0 cpu-migrations # 0.000 K/sec
105 page-faults # 0.010 K/sec
24,583,857,467 cycles # 2.300 GHz
27,117,299,405 instructions # 1.10 insn per cycle
6,571,204,123 branches # 614.782 M/sec
32,996,513 branch-misses # 0.50% of all branches
10.688907278 seconds time elapsed
问题:
我们可以看到cpu是相似的,os内核是相同的,但是为什么perf stat的周期如此不同
编辑:
我修改shell和命令:
x、 sh,将循环次数变小以减少花费的时间
i=0
while (( i < 10000 ))
do
(( i ++))
done
S2:
并发现rpm版本不同
性能差异显示:
# Event 'cycles'
#
# Baseline Delta Shared Object Symbol
# ........ ....... ................. ..............................................
#
21.20% +3.83% bash [.] 0x000000000002c0f0
10.22% libc-2.17.so [.] _int_free
9.11% libc-2.17.so [.] _int_malloc
7.97% libc-2.17.so [.] malloc
4.09% libc-2.17.so [.] __gconv_transform_utf8_internal
3.71% libc-2.17.so [.] __mbrtowc
3.48% -1.63% bash [.] execute_command_internal
3.48% +1.18% [unknown] [k] 0xfffffe0000032000
3.25% -1.87% bash [.] xmalloc
3.12% libc-2.17.so [.] __strcpy_sse2_unaligned
2.44% +2.22% [kernel.kallsyms] [k] syscall_return_via_sysret
2.09% -0.24% bash [.] evalexp
2.09% libc-2.17.so [.] __ctype_get_mb_cur_max
1.92% libc-2.17.so [.] free
1.41% -0.95% bash [.] dequote_string
1.19% +0.23% bash [.] stupidly_hack_special_variables
1.16% libc-2.17.so [.] __strlen_sse2_pminub
1.16% libc-2.17.so [.] __memcpy_ssse3_back
1.16% libc-2.17.so [.] __strcmp_sse42
0.93% -0.01% bash [.] mbschr
0.93% -0.47% bash [.] hash_search
0.70% libc-2.17.so [.] __sigprocmask
0.70% -0.23% bash [.] dispose_words
0.70% -0.23% bash [.] execute_command
0.70% -0.23% bash [.] set_pipestatus_array
0.70% bash [.] run_pending_traps
0.47% bash [.] malloc@plt
0.47% bash [.] var_lookup
0.47% bash [.] fmtumax
0.47% bash [.] do_redirections
0.46% bash [.] dispose_word
0.46% -0.00% bash [.] alloc_word_desc
0.46% -0.00% [kernel.kallsyms] [k] _copy_to_user
0.46% libc-2.17.so [.] __ctype_b_loc
0.46% bash [.] new_fd_bitmap
0.46% bash [.] add_unwind_protect
0.46% -0.00% bash [.] discard_unwind_frame
0.46% bash [.] memcpy@plt
0.46% bash [.] __ctype_get_mb_cur_max@plt
0.46% bash [.] signal_in_progress
0.40% libc-2.17.so [.] _IO_vfscanf
0.40% ld-2.17.so [.] do_lookup_x
0.27% bash [.] mbrtowc@plt
0.24% +1.60% [kernel.kallsyms] [k] __x64_sys_rt_sigprocmask
0.23% bash [.] list_append
0.23% bash [.] bind_variable
0.23% +0.69% [kernel.kallsyms] [k] entry_SYSCALL_64_stage2
0.23% +0.69% [kernel.kallsyms] [k] do_syscall_64
0.23% libc-2.17.so [.] _dl_mcount_wrapper_check
0.23% +0.69% bash [.] make_word_list
0.23% +0.69% [kernel.kallsyms] [k] copy_user_generic_unrolled
0.23% [kernel.kallsyms] [k] unmap_page_range
0.23% libc-2.17.so [.] __sigjmp_save
0.23% +0.23% [kernel.kallsyms] [k] entry_SYSCALL_64_after_hwframe
0.20% [kernel.kallsyms] [k] swapgs_restore_regs_and_return_to_usermode
0.03% [kernel.kallsyms] [k] page_fault
0.00% [kernel.kallsyms] [k] xfs_bmapi_read
0.00% [kernel.kallsyms] [k] xfs_release
0.00% +0.00% [kernel.kallsyms] [k] native_write_msr
+45.33% libc-2.17.so [.] 0x0000000000027cc6
+0.52% [kernel.kallsyms] [k] __mod_node_page_state
+0.46% bash [.] free@plt
+0.46% [kernel.kallsyms] [k] copy_user_enhanced_fast_string
+0.46% bash [.] begin_unwind_frame
+0.46% bash [.] make_bare_word
+0.46% bash [.] find_variable_internal
+0.37% ld-2.17.so [.] 0x0000000000009b13
也许glibc的差异就是答案强>
编辑:
最后,我检查了BIOS的配置,看到S2服务器使用了省电模式,这才是真正的答案
但是,BIOS的配置使我混淆了MONITOR-MWAIT,即使使用“最大性能模式”和“MONITOR-MWAIT”启用,S2的性能也很差。并使用命令cpupower idle info-o
,请参阅cpu使用“C状态”,该状态已在“最大性能模式”中禁用。它必须是禁用加上“最大性能模式”,性能才会更好
“MONITOR-MWAIT”的描述说,一些操作系统将检查此选项以恢复“C-state”,我找不到Linux内核如何使用它来更改“C-state”…我找到了答案
首先,让我们看看内核4.18.7中BIOS的MONITOR/MWAIT选项。
在该内核中,它将使用intel\u idle驱动程序,该驱动程序只检查系统是否支持mwait指令,而不关心是否启用了C状态。
一旦使用MONITOR/MWAIT指令,将使用intel_空闲驱动程序,并强制使用C状态,就像使用省电模式一样
第二,为什么每个周期的insn不同?
因为,使用了服务调谐,活动配置文件为“延迟性能”,强制延迟为1U。
如果使用C-state,将使用延迟小于force_延迟的C-state级别
# cpupower idle-info
CPUidle driver: intel_idle
CPUidle governor: menu
analyzing CPU 0:
Number of idle states: 5
Available idle states: POLL C1 C1E C3 C6
POLL:
Flags/Description: CPUIDLE CORE POLL IDLE
Latency: 0
Usage: 13034605
Duration: 820867557
C1:
Flags/Description: MWAIT 0x00
Latency: 2
Usage: 349471619
Duration: 344311623672
C1E:
Flags/Description: MWAIT 0x01
Latency: 10
Usage: 237
Duration: 55999
C3:
Flags/Description: MWAIT 0x10
Latency: 40
Usage: 350
Duration: 168988
C6:
Flags/Description: MWAIT 0x20
Latency: 133
Usage: 3696
Duration: 17809893
您将只看到延迟小于1U的轮询级别,轮询级别将强制CPU使用NOP指令运行。
在这种情况下,如果使用超线程技术,将使执行指令的速度下降一半。
因为两个逻辑核将共享一个ALU,并且其中一个正在运行NOP指令,所以导致另一个逻辑核必须等待它
如果禁用MONITOR/MWAIT选项,则intel_idle驱动程序将被禁用,因此将不使用调整后的服务的强制延迟,并且逻辑核心的一个将停止,使另一个使用ALU独占性
最后,感谢大家,特别是@Peter Cordes和@osgx,让我检查BIOS,命令
echo 2^1234567%2 | bc
非常漂亮 您确定这是上述脚本的输出吗?它只包含1百万个非常简单的迭代,但输出列出了数十亿个分支和5秒的总时间。是的,我确定!我认为,该脚本是一个shell脚本,因此它将被编译成更多的指令,因为它将调用内核,内核有更多的分支。请提供一个包含编译选项和编译器版本以及特定的perf
命令行的脚本。shell脚本不是可重复基准测试的良好基础。。。至少你必须提供shell和它的版本。。。请在你的帖子中包含这些信息,不要(仅)在评论中发表。进行更多的系统调用当然可以解释这一点。启用Spectre/Meldown缓解功能后,系统调用会有很大的开销,由于TLB收回,在返回后的一段时间内,一切都会变慢。也许bash正在分配/释放内存,在速度较慢的机器上,它决定每次都将内存返回操作系统,而不是将其保留在空闲列表中。如果您为libc安装调试符号,您能分析在libc中花费的大量时间吗?
/usr/lib64/ld-2.17.so with build id 93d2e4a501823d041413eeb652b89044d1f680ee not found, continuing without symbols
/usr/lib64/libc-2.17.so with build id b04a54c443d36058702ab4060c63f4ab3273eae9 not found, continuing without symbols
# Event 'cycles'
#
# Baseline Delta Shared Object Symbol
# ........ ....... ................. ..............................................
#
21.20% +3.83% bash [.] 0x000000000002c0f0
10.22% libc-2.17.so [.] _int_free
9.11% libc-2.17.so [.] _int_malloc
7.97% libc-2.17.so [.] malloc
4.09% libc-2.17.so [.] __gconv_transform_utf8_internal
3.71% libc-2.17.so [.] __mbrtowc
3.48% -1.63% bash [.] execute_command_internal
3.48% +1.18% [unknown] [k] 0xfffffe0000032000
3.25% -1.87% bash [.] xmalloc
3.12% libc-2.17.so [.] __strcpy_sse2_unaligned
2.44% +2.22% [kernel.kallsyms] [k] syscall_return_via_sysret
2.09% -0.24% bash [.] evalexp
2.09% libc-2.17.so [.] __ctype_get_mb_cur_max
1.92% libc-2.17.so [.] free
1.41% -0.95% bash [.] dequote_string
1.19% +0.23% bash [.] stupidly_hack_special_variables
1.16% libc-2.17.so [.] __strlen_sse2_pminub
1.16% libc-2.17.so [.] __memcpy_ssse3_back
1.16% libc-2.17.so [.] __strcmp_sse42
0.93% -0.01% bash [.] mbschr
0.93% -0.47% bash [.] hash_search
0.70% libc-2.17.so [.] __sigprocmask
0.70% -0.23% bash [.] dispose_words
0.70% -0.23% bash [.] execute_command
0.70% -0.23% bash [.] set_pipestatus_array
0.70% bash [.] run_pending_traps
0.47% bash [.] malloc@plt
0.47% bash [.] var_lookup
0.47% bash [.] fmtumax
0.47% bash [.] do_redirections
0.46% bash [.] dispose_word
0.46% -0.00% bash [.] alloc_word_desc
0.46% -0.00% [kernel.kallsyms] [k] _copy_to_user
0.46% libc-2.17.so [.] __ctype_b_loc
0.46% bash [.] new_fd_bitmap
0.46% bash [.] add_unwind_protect
0.46% -0.00% bash [.] discard_unwind_frame
0.46% bash [.] memcpy@plt
0.46% bash [.] __ctype_get_mb_cur_max@plt
0.46% bash [.] signal_in_progress
0.40% libc-2.17.so [.] _IO_vfscanf
0.40% ld-2.17.so [.] do_lookup_x
0.27% bash [.] mbrtowc@plt
0.24% +1.60% [kernel.kallsyms] [k] __x64_sys_rt_sigprocmask
0.23% bash [.] list_append
0.23% bash [.] bind_variable
0.23% +0.69% [kernel.kallsyms] [k] entry_SYSCALL_64_stage2
0.23% +0.69% [kernel.kallsyms] [k] do_syscall_64
0.23% libc-2.17.so [.] _dl_mcount_wrapper_check
0.23% +0.69% bash [.] make_word_list
0.23% +0.69% [kernel.kallsyms] [k] copy_user_generic_unrolled
0.23% [kernel.kallsyms] [k] unmap_page_range
0.23% libc-2.17.so [.] __sigjmp_save
0.23% +0.23% [kernel.kallsyms] [k] entry_SYSCALL_64_after_hwframe
0.20% [kernel.kallsyms] [k] swapgs_restore_regs_and_return_to_usermode
0.03% [kernel.kallsyms] [k] page_fault
0.00% [kernel.kallsyms] [k] xfs_bmapi_read
0.00% [kernel.kallsyms] [k] xfs_release
0.00% +0.00% [kernel.kallsyms] [k] native_write_msr
+45.33% libc-2.17.so [.] 0x0000000000027cc6
+0.52% [kernel.kallsyms] [k] __mod_node_page_state
+0.46% bash [.] free@plt
+0.46% [kernel.kallsyms] [k] copy_user_enhanced_fast_string
+0.46% bash [.] begin_unwind_frame
+0.46% bash [.] make_bare_word
+0.46% bash [.] find_variable_internal
+0.37% ld-2.17.so [.] 0x0000000000009b13
# cpupower idle-info
CPUidle driver: intel_idle
CPUidle governor: menu
analyzing CPU 0:
Number of idle states: 5
Available idle states: POLL C1 C1E C3 C6
POLL:
Flags/Description: CPUIDLE CORE POLL IDLE
Latency: 0
Usage: 13034605
Duration: 820867557
C1:
Flags/Description: MWAIT 0x00
Latency: 2
Usage: 349471619
Duration: 344311623672
C1E:
Flags/Description: MWAIT 0x01
Latency: 10
Usage: 237
Duration: 55999
C3:
Flags/Description: MWAIT 0x10
Latency: 40
Usage: 350
Duration: 168988
C6:
Flags/Description: MWAIT 0x20
Latency: 133
Usage: 3696
Duration: 17809893