BogoMips

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BogoMips ("bogus" 和MIPS, 伪MIPS) 是一种衡量CPU速度的不科学的方法。当计算机内核启动时,将执行一个计数循环。

对于特定的CPU,BogoMips可用来查看它是否是个合适的值.它的时钟频率和它潜在的CPU缓存。但是它不可在不同的CPU间进行比较演示。[1]

合适的BogoMips比率[编辑]

作为一个参考向导,BogoMips可以用下列的表格进行预计算。给出的比率是以应用到LINUX版本的CPU作为例子。指数是指其它CPU同Intel 386DX CPU的BogoMips/clock speed比率.

CPU 比率 指数
Intel 8088 clock * 0.004 0.02
Intel/AMD 386SX clock * 0.14 0.8
Intel/AMD 386DX clock * 0.18 1 (definition)
Motorola 68030 clock * 0.25 1.4
Cyrix/IBM 486 clock * 0.34 1.8
Intel Pentium clock * 0.40 2.2
Intel 486 clock * 0.50 2.8
AMD 5x86 clock * 0.50 2.8
MIPS R4000/R4400 clock * 0.50 2.8
ARM9 clock * 0.50 2.8
Motorola 8081 clock * 0.65 3.6
Motorola 68040 clock * 0.67 3.7
PowerPC 603 clock * 0.67 3.7
Intel StrongARM clock * 0.66 3.7
NexGen Nx586 clock * 0.75 4.2
PowerPC 601 clock * 0.84 4.7
Alpha 21064/21064A clock * 0.99 5.5
Alpha 21066/21066A clock * 0.99 5.5
Alpha 21164/21164A clock * 0.99 5.5
Intel Pentium Pro clock * 0.99 5.5
Cyrix 5x86/6x86 clock * 1.00 5.6
Intel Pentium II/III clock * 1.00 5.6
AMD K7/Athlon clock * 1.00 5.6
Intel Celeron clock * 1.00 5.6
Intel Itanium clock * 1.00 5.6
R4600 clock * 1.00 5.6
Hitachi SH-4 clock * 1.00 5.6
Intel Itanium 2 clock * 1.49 8.3
Alpha 21264 clock * 1.99 11.1
VIA Centaur clock * 1.99 11.1
AMD K5/K6/K6-2/K6-III clock * 2.00 11.1
AMD Duron/Athlon XP clock * 2.00 11.1
AMD Sempron clock * 2.00 11.1
UltraSparc II clock * 2.00 11.1
Intel Pentium MMX clock * 2.00 11.1
Intel Pentium 4 clock * 2.00 11.1
Intel Pentium M clock * 2.00 11.1
Intel Core Duo clock * 2.00 11.1
Intel Core 2 Duo clock * 2.00 11.1
Intel Atom N455 clock * 2.00 11.1
Centaur C6-2 clock * 2.00 11.1
PowerPC 604/604e/750 clock * 2.00 11.1
Intel Pentium III Coppermine clock * 2.00 11.1
Intel Pentium III Xeon clock * 2.00 11.1
Motorola 68060 clock * 2.01 11.2
Intel Xeon MP (32-bit) (hyper-threading) clock * 3.97 22.1
IBM S390 not enough data (yet)
ARM not enough data (yet)

BogoMIPS 怎么计算的?[编辑]

在当前内核(2.6.x),BogoMIPS实现在内核源文件/usr/src/linux/init/calibrate.c。它计算了Linux内核定时参数loops_per_jiffy (see Jiffy (time) ) 值。源码解释如下:

 /*
   * A simple loop like
   *  while ( jiffies < start_jiffies+1)
   *    start = read_current_timer();
   * will not do. As we don't really know whether jiffy switch
   * happened first or timer_value was read first. And some asynchronous
   * event can happen between these two events introducing errors in lpj.
   *
   * So, we do
   * 1. pre_start <- When we are sure that jiffy switch hasn't happened
   * 2. check jiffy switch
   * 3. start <- timer value before or after jiffy switch
   * 4. post_start <- When we are sure that jiffy switch has happened
   *
   * Note, we don't know anything about order of 2 and 3.
   * Now, by looking at post_start and pre_start difference, we can
   * check whether any asynchronous event happened or not
   */

loops_per_jiffy is used to implement udelay (delay in microseconds) and ndelay (delay in nanoseconds) functions. These functions are needed by some drivers to wait for hardware. Note that a busy waiting technique is used, so the kernel is effectively blocked when executing ndelay/udelay functions. For i386 architecture delay_loop is implemented in /usr/src/linux/arch/i386/lib/delay.c as:

/* simple loop based delay: */
static void delay_loop(unsigned long loops)
{
  int d0;
 
  __asm__ __volatile__(
    "\tjmp 1f\n"
    ".align 16\n"
    "1:\tjmp 2f\n"
    ".align 16\n"
    "2:\tdecl %0\n\tjns 2b"
    :"=&a" (d0)
    :"0" (loops));
}

用C语言重写的代码如下:

static void delay_loop(long loops)
{
  long d0 = loops;
  do {
    --d0;
  } while (d0 >= 0);
}

关于BogoMips更丰富更全的信息和数百篇相关文章可参见 BogoMips mini-Howto.[1]

参考[编辑]

  1. ^ 1.0 1.1 Van Dorst, Wim. BogoMips Mini-Howto V38. 2 March 2006 [2008-08-22]. 

外部链接[编辑]