lkml.org 
[lkml]   [2008]   [Dec]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC v11][PATCH 05/13] Dump memory address space


Dave Hansen wrote:
> On Thu, 2008-12-18 at 06:10 -0500, Oren Laadan wrote:
>>>> + for (i = pgarr->nr_used; i--; /**/)
>>>> + page_cache_release(pgarr->pages[i]);
>>> This is sorta hard to read (and non-intuitive). Is it easier to do:
>>>
>>> for (i = 0; i < pgarr->nr_used; i++)
>>> page_cache_release(pgarr->pages[i]);
>>>
>>> It shouldn't matter what order you release the pages in..
>> Was meant to avoid a dereference to 'pgarr->nr_used' in the comparison.
>> (though I doubt if the performance impact is at all visible)
>
> That's a bit to aggressive an optimization. You two piqued my
> curiosity, so I tried a little experiment with this .c file:
>
> extern void bar(int i);
>
> struct s {
> int *array;
> int size;
> };
>
> extern struct s *s;
> void foo(void)
> {
> int i;
> #ifdef OREN
> for (i = s->size; i--; )
> #else
> for (i = 0; i < s->size; i++)
> #endif
> bar(s->array[i]);
> }
>
> for O in "" -O -O1 -O2 -O3 -Os; do
> gcc -DOREN $O -c f1.c -o oren.o;
> gcc $O -c f1.c -o mike.o;
> echo -n Oren:; objdump -d oren.o | grep ret;
> echo -n Mike:; objdump -d mike.o | grep ret;
> done

For what it's worth, the idea was to improve time... (not code length).
I changed the code anyway (in response to another comment).

Oren.



\
 
 \ /
  Last update: 2008-12-18 21:03    [from the cache]
©2003-2014 Jasper Spaans. Advertise on this site