Re: [PATCH] crypto/xor.c: use 2 pages for xor speed testing

[Amos Kong <akong@redhat.com>]

On Thu, Jun 05, 2014 at 11:57:55PM +0200, Marek Vasut wrote:
> On Thursday, June 05, 2014 at 03:11:33 AM, Amos Kong wrote:
> > In crypto/xor.c: calibrate_xor_blocks(), we allocated total 4 pages to
> > do xor speed testing, the BENCH_SIZE is 1 page, and we skipped 2 pages
> > when we set b2.
> > 
> > It seems that total 2 pages are enough without skipping 2 pages.
> > 
> > Signed-off-by: Amos Kong <akong@redhat.com>
> > ---
> >  crypto/xor.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/crypto/xor.c b/crypto/xor.c
> > index 35d6b3a..609dfb5 100644
> > --- a/crypto/xor.c
> > +++ b/crypto/xor.c
> > @@ -114,12 +114,12 @@ calibrate_xor_blocks(void)
> >  	 * test the XOR speed, we don't really want kmemcheck to warn about
> >  	 * reading uninitialized bytes here.
> >  	 */
> > -	b1 = (void *) __get_free_pages(GFP_KERNEL | __GFP_NOTRACK, 2);
> > +	b1 = (void *) __get_free_pages(GFP_KERNEL | __GFP_NOTRACK, 1);
> >  	if (!b1) {
> >  		printk(KERN_WARNING "xor: Yikes!  No memory available.\n");
> >  		return -ENOMEM;
> >  	}
> > -	b2 = b1 + 2*PAGE_SIZE + BENCH_SIZE;
> > +	b2 = b1 + BENCH_SIZE;
> > 
> >  	/*
> >  	 * If this arch/cpu has a short-circuited selection, don't loop through
> > @@ -154,7 +154,7 @@ calibrate_xor_blocks(void)
> >  #undef xor_speed
> > 
> >   out:
> > -	free_pages((unsigned long)b1, 2);
> > +	free_pages((unsigned long)b1, 1);
> > 
> >  	active_template = fastest;
> >  	return 0;
> 
> I think this does make sense, but I am not 100% sure, sorry.
> 
> ...
> 
> While looking at this code, can anyone explain to me why we have this stuff in 
> crypto/xor.c please ?
> 
> 135 #define xor_speed(templ)        do_xor_speed((templ), b1, b2)
> 136 
> 137         if (fastest) {
> 138                 printk(KERN_INFO "xor: automatically using best "
> 139                                  "checksumming function:\n");
> 140                 xor_speed(fastest);
> 141                 goto out;
> 142         } else {
> [...]
> 149         }
> 150 
> 151         printk(KERN_INFO "xor: using function: %s (%d.%03d MB/sec)\n",
> 152                fastest->name, fastest->speed / 1000, fastest->speed % 1000);
> 153 
> 154 #undef xor_speed
> 
> Why do we not call do_xor_speed(fastest, b1, b2); right away , but we #define 
> xor_speed() instead ? This looks like some remnant or nonsense to me. Shall I 
> remove that with a patch ?

You are right.
 
> Best regards,
> Marek Vasut

-- 
			Amos.