Messages in this thread | | | Subject | Re: [PATCH v2 2/2] x86: add prefetching to do_csum | From | Joe Perches <> | Date | Fri, 08 Nov 2013 11:17:39 -0800 |
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On Fri, 2013-11-08 at 14:07 -0500, Neil Horman wrote: > On Fri, Nov 08, 2013 at 08:51:07AM -0800, Joe Perches wrote: > > On Fri, 2013-11-08 at 11:25 -0500, Neil Horman wrote: > > > On Wed, Nov 06, 2013 at 12:07:38PM -0800, Joe Perches wrote: > > > > On Wed, 2013-11-06 at 15:02 -0500, Neil Horman wrote: > > > > > On Wed, Nov 06, 2013 at 09:19:23AM -0800, Joe Perches wrote: > > > > [] > > > > > > __always_inline instead of inline > > > > > > static __always_inline void prefetch_lines(const void *addr, size_t len) > > > > > > { > > > > > > const void *end = addr + len; > > > > > > ... > > > > > > > > > > > > buff doesn't need a void * cast in prefetch_lines > > > > > > > > > > > Actually I take back what I said here, we do need the cast, not for a conversion > > > > > from unsigned char * to void *, but rather to discard the const qualifier > > > > > without making the compiler complain. > > > > > > > > Not if the function is changed to const void * > > > > and end is also const void * as shown. > > > > > > > Addr is incremented in the for loop, so it can't be const. I could add a loop > > > counter variable on the stack, but that doesn't seem like it would help anything > > > > Perhaps you meant > > void * const addr; > > but that's not what I wrote. > > > No, I meant smoething like: > static __always_inline void prefetch_lines(const void * addr, size_t len) > { > const void *tmp = (void *)addr; > ... > for(;tmp<end; tmp+=cache_line_size()) > ... > } > > > Let me know if this doesn't compile. > > It does here... > Huh, it does. But that makes very little sense to me. by qualifying addr as > const, how is the compiler not throwing a warning in the for loop about us > incrementing that same variable?
Because it points to const data but is not const itself.
void * const foo; /* value of foo can't change */ const void *bar; /* data pointed to by bar can't change */ const void * const baz; /* Neither baz nor data pointed to by baz can change */
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