Messages in this thread | | | Date | Mon, 10 Mar 2008 19:39:55 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH REPOST for 2.6.25] Use an own random generator for pageattr-test.c |
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On Tue, 11 Mar 2008 02:30:14 +0100 Andi Kleen <andi@firstfloor.org> wrote:
> Use an own random generator for pageattr-test.c > > [Repost. Please ack/nack. This is a bug fix and imho a .25 late merge > candidate because it fixes a subtle bug]
An Ingo/Thomas thing.
> pageattr-test attempts to be repeatable and uses srandom32 to get a > repeatable random number sequence. > > Using srandom32() wasn't a good idea for various reasons: > - it is per cpu and if the cpu changes on a preemptible kernel it gets lost > - networking and random32 puts in some own state > - srandom32() does not actually reset the state, but just adds bits to > it > > Instead use a very simple private standard rnd that gives repeatable > results. I took the reference rand() from ISO-C. > > Signed-off-by: Andi Kleen <ak@suse.de> > > --- > arch/x86/mm/pageattr-test.c | 11 +++++++++-- > 1 file changed, 9 insertions(+), 2 deletions(-) > > Index: linux/arch/x86/mm/pageattr-test.c > =================================================================== > --- linux.orig/arch/x86/mm/pageattr-test.c > +++ linux/arch/x86/mm/pageattr-test.c > @@ -101,6 +101,14 @@ static int print_split(struct split_stat > static unsigned long addr[NTEST]; > static unsigned int len[NTEST]; > > +static int next = 100; > + > +static unsigned my_rand(void) > +{ > + next = next * 1103515245 + 12345; > + return next; > +}
`next' should be local to my_rand().
> /* Change the global bit on random pages in the direct mapping */ > static int pageattr_test(void) > { > @@ -123,10 +131,9 @@ static int pageattr_test(void) > memset(bm, 0, (max_pfn_mapped + 7) / 8); > > failed += print_split(&sa); > - srandom32(100); > > for (i = 0; i < NTEST; i++) { > - unsigned long pfn = random32() % max_pfn_mapped; > + unsigned long pfn = my_rand() % max_pfn_mapped; > > addr[i] = (unsigned long)__va(pfn << PAGE_SHIFT); > len[i] = random32() % 100;
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