linux-kernel - Re: [OT] Argument with an OS professor over profile=3

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Date:	Thu, 11 Oct 2007 11:06:08 +0930
From:	David Newall <david@...idnewall.com>
To:	Russ Dill <russ.dill@...il.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: [OT] Argument with an OS professor over profile=3

Russ Dill wrote:
> I've been having a back and forth going for a while with my TA and OS
> professor on the meaning of profile=3 and have been unable to convince
> either of them. The basic question is if profile=3 is passed to kernel
> with an 8MB text section, how big is the allocated profile buffer. His
> answer is 1MB....
>
>         if (prof_shift) {
>                 unsigned int size;
>                 /* only text is profiled */
>                 prof_len = (unsigned *) &_etext - (unsigned *) &_stext;
>   
You stipulated 8MB text, but this calculates in unsigned ints, so 
prof_len = 2M.

>                 prof_len >>= prof_shift;
>   

This gives 250K (divide by 8).

>                 size = prof_len * sizeof(unsigned int) + PAGE_SIZE-1;
>   

Finally, size is 1MB (250K x 4).

>                 prof_buffer = (unsigned int *) alloc_bootmem(size);
>         }
>   

I'm with your Prof.  Perhaps you missed that prof_len counts integers, 
not bytes.
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