BogoMips
BogoMips ("bogus" 和MIPS, 伪MIPS) 是一种衡量CPU速度的不科学方法。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
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?
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
- Van Dorst, Wim. V38. 2 March 2006 [2008-08-22]. （原始内容存档于2013-08-27）.
外部链接
- BogoMips Mini-Howto, V38Archived 2013-08-27 at WebCite