Query about loops_per_jiffy

[胡杨树]

Are you  Alessandro Rubini of LINUX DEVICE DRIVER?


------------------ Original ------------------
From:  "Alessandro Rubini"<rubini-list at gnudd.com>;
Date:  Tue, Jan 19, 2010 04:21 PM
To:  "914059751"<914059751 at qq.com>; 
Cc:  "linux-arm-kernel"<linux-arm-kernel at lists.infradead.org>; 
Subject:  Re: Query about loops_per_jiffy

 
 > (loops_per_jiffy * HZ)/1000,000   will give a BogoMips value.

No, it will give a BogoLips (loops per second). A loop is two instructions,
in ./arch/arm/lib/delay.S (function __delay) called by init/calibrate.c .
To have bogomips you need to multiply by two.

> then why calibrate_delay do it like the following:
>     printk(KERN_CONT "%lu.%02lu BogoMIPS (lpj=%lu)\n",
>             loops_per_jiffy/(500000/HZ),
>             (loops_per_jiffy/(5000/HZ)) % 100, loops_per_jiffy);

It's correct, using normal integer aritmetics care.

/alessandro
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