KVM性能分析工具

本文介绍了如何使用perf工具跟踪和统计KVM事件,包括kvm_entry、kvm_exit等关键事件的计数,并展示了如何记录和分析KVM性能数据,特别强调了在内核版本3.7以上进行KVM事件的详细分析,如VMEXIT、MMIO和IOPORT事件,以及按时间排序的vcpu事件分析。

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跟踪KVM事件

# echo 1 >/sys/kernel/debug/tracing/events/kvm/enable
# cat /sys/kernel/debug/tracing/trace_pipe
[...]
             kvm-5664  [000] 11906.220178: kvm_entry: vcpu 0
             kvm-5664  [000] 11906.220181: kvm_exit: reason apic_access rip 0xc011518c
             kvm-5664  [000] 11906.220183: kvm_mmio: mmio write len 4 gpa 0xfee000b0 val 0x0
             kvm-5664  [000] 11906.220183: kvm_apic: apic_write APIC_EOI = 0x0
             kvm-5664  [000] 11906.220184: kvm_ack_irq: irqchip IOAPIC pin 11
             kvm-5664  [000] 11906.220185: kvm_entry: vcpu 0
             kvm-5664  [000] 11906.220188: kvm_exit: reason io_instruction rip 0xc01e4473
             kvm-5664  [000] 11906.220188: kvm_pio: pio_read at 0xc13e size 2 count 1
             kvm-5664  [000] 11906.220193: kvm_entry: vcpu 0
^D
# echo 0 >/sys/kernel/debug/tracing/events/kvm/enable

统计KVM事件

[root@localhost win7]# perf stat -e 'kvm:*' -a sleep 1h
^Csleep: Interrupt

 Performance counter stats for 'sleep 1h':

             1,880 kvm:kvm_entry                                                [100.00%]
                 0 kvm:kvm_hypercall                                            [100.00%]
                 0 kvm:kvm_hv_hypercall                                      [100.00%]
                20 kvm:kvm_pio                                                     [100.00%]
                 0 kvm:kvm_cpuid                                                  [100.00%]
               596 kvm:kvm_apic                                                  [100.00%]
             1,934 kvm:kvm_exit                                                  [100.00%]
               284 kvm:kvm_inj_virq                                             [100.00%]
                 3 kvm:kvm_inj_exception                                     [100.00%]
               602 kvm:kvm_page_fault                                       [100.00%]
                 0 kvm:kvm_msr                                                      [100.00%]
               102 kvm:kvm_cr                                                       [100.00%]
               260 kvm:kvm_pic_set_irq                                      [100.00%]
               156 kvm:kvm_apic_ipi                                            [100.00%]
               292 kvm:kvm_apic_accept_irq                              [100.00%]
               292 kvm:kvm_eoi                                                     [100.00%]
                 0 kvm:kvm_pv_eoi                                                 [100.00%]
                 0 kvm:kvm_nested_vmrun                                   [100.00%]
                 0 kvm:kvm_nested_intercepts                             [100.00%]
                 0 kvm:kvm_nested_vmexit                                    [100.00%]
                 0 kvm:kvm_nested_vmexit_inject                        [100.00%]
                 0 kvm:kvm_nested_intr_vmexit                            [100.00%]
                 0 kvm:kvm_invlpga                                                 [100.00%]
                 0 kvm:kvm_skinit                                                    [100.00%]
               979 kvm:kvm_emulate_insn                                  [100.00%]
               618 kvm:vcpu_match_mmio                                  [100.00%]
               635 kvm:kvm_userspace_exit                               [100.00%]
               276 kvm:kvm_set_irq                                              [100.00%]
               276 kvm:kvm_ioapic_set_irq                                 [100.00%]
                 4 kvm:kvm_msi_set_irq                                        [100.00%]
               277 kvm:kvm_ack_irq                                              [100.00%]
             1,627 kvm:kvm_mmio                                                [100.00%]
               762 kvm:kvm_fpu                                                      [100.00%]
                 0 kvm:kvm_age_page                                            [100.00%]
                 0 kvm:kvm_try_async_get_page                          [100.00%]
                 0 kvm:kvm_async_pf_doublefault                        [100.00%]
                 0 kvm:kvm_async_pf_not_present                      [100.00%]
                 0 kvm:kvm_async_pf_ready                                  [100.00%]
                 0 kvm:kvm_async_pf_completed                                   

       1.895712367 seconds time elapsed

KVM性能数据记录与分析 (需要kernel > 3.7)


记录性能数据

# ./perf kvm stat record -p 26071 -o perf.data
^C[ perf record: Woken up 9 times to write data ]
[ perf record: Captured and wrote 24.903 MB perf.data.guest (~1088034 samples) ]

分析VMEXIT事件

# ./perf kvm stat report --event=vmexit

Analyze events for all VCPUs:

             VM-EXIT    Samples  Samples%     Time%         Avg time

         APIC_ACCESS      65381    66.58%     5.95%     37.72us ( +-   6.54% )
  EXTERNAL_INTERRUPT      16031    16.32%     3.06%     79.11us ( +-   7.34% )
               CPUID       5360     5.46%     0.06%      4.50us ( +-  35.07% )
                 HLT       4496     4.58%    90.75%   8360.34us ( +-   5.22% )
       EPT_VIOLATION       2667     2.72%     0.04%      5.49us ( +-   5.05% )
   PENDING_INTERRUPT       2242     2.28%     0.03%      5.25us ( +-   2.96% )
       EXCEPTION_NMI       1332     1.36%     0.02%      6.53us ( +-   6.51% )
      IO_INSTRUCTION        383     0.39%     0.09%     93.39us ( +-  40.92% )
           CR_ACCESS        310     0.32%     0.00%      6.10us ( +-   3.95% )

Total Samples:98202, Total events handled time:41419293.63us.

分析MMIO事件

# ./perf kvm stat report --event=mmio

Analyze events for all VCPUs:

         MMIO Access    Samples  Samples%     Time%         Avg time

        0xfee00380:W      58686    90.21%    15.67%      4.95us ( +-   2.96% )
        0xfee00300:R       2124     3.26%     1.48%     12.93us ( +-  14.75% )
        0xfee00310:W       2124     3.26%     0.34%      3.00us ( +-   1.33% )
        0xfee00300:W       2123     3.26%    82.50%    720.68us ( +-  10.24% )

Total Samples:65057, Total events handled time:1854470.45us.

分析IOPORT事件

# ./perf kvm stat report --event=ioport

Analyze events for all VCPUs:

      IO Port Access    Samples  Samples%     Time%         Avg time

         0xc090:POUT        383   100.00%   100.00%     89.00us ( +-  42.94% )

Total Samples:383, Total events handled time:34085.56us.

针对指定的vcpu分析事件,并按照时间来排序输出结果

# ./perf kvm stat report --event=vmexit --vcpu=0 --key=time

Analyze events for VCPU 0:

             VM-EXIT    Samples  Samples%     Time%         Avg time

                 HLT        551     5.05%    94.81%   9501.72us ( +-  12.52% )
  EXTERNAL_INTERRUPT       1390    12.74%     2.39%     94.80us ( +-  20.92% )
         APIC_ACCESS       6186    56.68%     2.62%     23.41us ( +-  23.62% )
      IO_INSTRUCTION         17     0.16%     0.01%     20.39us ( +-  22.33% )
       EXCEPTION_NMI         94     0.86%     0.01%      6.07us ( +-   7.13% )
   PENDING_INTERRUPT        199     1.82%     0.02%      5.48us ( +-   4.36% )
           CR_ACCESS         52     0.48%     0.00%      4.89us ( +-   4.09% )
       EPT_VIOLATION       2057    18.85%     0.12%      3.15us ( +-   1.33% )
               CPUID        368     3.37%     0.02%      2.82us ( +-   2.79% )

Total Samples:10914, Total events handled time:5521782.02us.


<think>嗯,用户想了解CRC32校验算法的实现和使用方法。我需要先回顾一下CRC32的基本原理,然后考虑如何用简单易懂的中文解释清楚。首先,CRC32是基于循环冗余校验的一种算法,主要用于检测数据传输或存储中的错误。用户可能希望知道它的具体步骤,比如如何初始化、处理数据、异或操作以及最终得到校验值。 根据提供的引用资料,CRC32的核心是多项式除法,但实际中通过查表法优化速度。需要解释生成多项式,比如常见的0xEDB88320,以及初始值、输入输出是否反转这些参数。用户提供的代码片段中有两个版本,一个是逐位计算,另一个是查表法,这可能需要在回答中对比说明,突出查表法的效率优势。 接下来,用户可能关心具体怎么使用这个算法,比如在C语言中的实现步骤,或者如何应用到实际项目中,比如文件校验或网络传输。要分步骤讲解,从初始化到处理每个字节,再到最终计算,可能需要示例代码来辅助说明。同时,注意用户要求行内数学表达式用$...$,比如多项式应该写成$0xEDB88320$这样的格式。 另外,用户的问题里提到生成相关问题,我需要考虑相关的问题可能涉及性能优化、不同生成多项式的影响,或者CRC32与其他校验算法的比较。这些可以作为相关问题放在最后,帮助用户进一步探索。 需要确保回答结构清晰,先讲原理,再讲实现步骤,然后使用方法,最后附上相关问题。同时,引用提供的资料,比如引用[^1]和[^2]来支持解释。要避免技术术语过于复杂,保持语言通俗易懂,同时满足LaTeX格式要求,比如多项式用$符号包裹。检查是否有遗漏的步骤,比如输入反转和输出反转的处理,这在代码示例中有所体现,需要解释清楚这些参数的作用。</think>### CRC32校验算法实现及使用方法 #### 一、CRC32基本原理 CRC32通过多项式除法生成32位校验值,用于检测数据传输或存储中的错误。其核心是生成多项式$G(x)$,常用标准为$0xEDB88320$(反向多项式形式)[^1]。算法流程如下: 1. **初始化**:设置32位寄存器初值为$0xFFFFFFFF$ 2. **数据输入**:逐字节与寄存器异或运算 3. **位移处理**:根据多项式进行循环移位和异或操作 4. **结果取反**:最终值与$0xFFFFFFFF$异或 #### 二、算法实现(C语言) ```c // 查表法实现(高效) uint32_t crc32_table[256]; void init_crc32_table() { for (int i = 0; i < 256; i++) { uint32_t crc = i; for (int j = 0; j < 8; j++) { crc = (crc >> 1) ^ ((crc & 1) ? 0xEDB88320 : 0); } crc32_table[i] = crc; } } uint32_t calc_crc32(uint8_t *data, size_t len) { uint32_t crc = 0xFFFFFFFF; while (len--) { crc = (crc >> 8) ^ crc32_table[(crc ^ *data++) & 0xFF]; } return crc ^ 0xFFFFFFFF; } ``` 此实现通过预先生成的256元素查找表,将时间复杂度从$O(n \cdot 8)$优化到$O(n)$。 #### 三、使用场景及方法 1. **文件校验**:计算文件CRC32值验证完整性 ```bash $ crc32 filename.txt ``` 2. **网络传输**:在数据帧尾部附加4字节校验码 3. **存储系统**:RAID、ZFS等文件系统使用CRC32校验数据块 #### 四、参数配置 | 参数 | 说明 | 标准值 | |---------------|---------------------------|-----------------| | 初始值 | 寄存器初始状态 | 0xFFFFFFFF | | 多项式 | 生成多项式 | 0xEDB88320 | | 输入/输出反转 | 字节处理顺序 | 通常需要反转 |
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