From: Al Boldi <a1426z@gawab.com>
To: Arjan van de Ven <arjan@infradead.org>
Cc: Frank van Maarseveen <frankvm@frankvm.com>,
linux-kernel@vger.kernel.org, Andi Kleen <ak@suse.de>
Subject: Re: [PATCH] x86: Don't randomize stack unless current->personality permits it
Date: Sat, 15 Jul 2006 17:09:45 +0300 [thread overview]
Message-ID: <200607151709.45870.a1426z@gawab.com> (raw)
In-Reply-To: <1152966159.3114.19.camel@laptopd505.fenrus.org>
Arjan van de Ven wrote:
> On Sat, 2006-07-15 at 14:29 +0300, Al Boldi wrote:
> > Arjan van de Ven wrote:
> > > > BTW, why does randomize_stack_top() mod against (8192*1024) instead
> > > > of (8192) like arch_align_stack()?
> > >
> > > because it wants to randomize for 8Mb, unlike arch_align_stack which
> > > wants to randomize the last 8Kb within this 8Mb ;)
> >
> > Randomizing twice?
>
> a VMA can only be randomized in 4Kb (well page size) granularity, so the
> 8Mb randomization can only work in that 4Kb unit, the "second"
> randomization can work in 16 byte granularity.
>
> > There is even a case where a mere rename or running through an extra
> > shell causes a slowdown. And that's with randomization turned off.
>
> randomization off will slow stuff down yes... you get cache alias
> contention that way.
Randomization on. Executable runs with 8x blips/hits.
Randomization off. Executable runs without blips/hits.
With randomization off, a mere rename causes an 8x-slowdown to occur. Run
this renamed executable through sh -c ./tstExec, and the slowdown
disappears. Really weired :)
> > 2.4.31 doesn't show these slowdowns.
>
> 2.4.31 randomizes the stack with 8Kb.
>
> > What is 2.6 doing?
>
> you're not providing a lot of info ;)
>
> why do you suspect randomization as cause for whatever slowdown you are
> seeing?
echo 0 > /proc/sys/kernel/randomize_va_space makes the blips/hits to go away,
most of the time.
> What kind of slowdown are you seeing?
see below.
Beware, this is highly compiler/glibc/distribution dependent.
My test environment is mdk9.1, gcc-3.2.2-3, 2.6.17.4, compile with -Os switch
Confirmed on rhel4, gcc-4.0.1, 2.6.9-5.EL, compile with no switches
Thanks!
--
Al
---
#include <stdio.h>
#include <sys/time.h>
unsigned long elapsed(int start) {
static struct timeval s,e;
if (start) return gettimeofday(&s, NULL);
gettimeofday(&e, NULL);
return ((e.tv_sec - s.tv_sec) * 1000 + (e.tv_usec - s.tv_usec) / 1000);
}
void fn2(double *x, double *y) {
*x = *y;
}
void fn() {
long i = 9999999;
double x,y;
elapsed(1);
while (i--) fn2(&x,&y);
printf("%4lu ",elapsed(0));
}
int main(int argc, char **argv) {
fn();
fn();
fn();
fn();
fn();
fn();
fn();
fn();
fn();
fn();
printf("msec\n");
return 0;
}
next prev parent reply other threads:[~2006-07-15 14:09 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-07-11 19:57 [PATCH] x86: Don't randomize stack unless current->personality permits it Al Boldi
2006-07-12 16:03 ` Andi Kleen
2006-07-12 20:12 ` Al Boldi
2006-07-12 20:27 ` Arjan van de Ven
2006-07-12 21:13 ` Al Boldi
2006-07-13 9:44 ` Frank van Maarseveen
2006-07-13 20:51 ` Al Boldi
2006-07-13 20:54 ` Arjan van de Ven
2006-07-15 11:29 ` Al Boldi
2006-07-15 12:22 ` Arjan van de Ven
2006-07-15 14:09 ` Al Boldi [this message]
2006-07-15 16:15 ` Arjan van de Ven
2006-07-15 17:39 ` Al Boldi
2006-07-17 15:50 ` Paulo Marques
2006-07-18 5:21 ` Al Boldi
-- strict thread matches above, loose matches on Subject: below --
2006-07-25 0:21 Chuck Ebbert
2006-07-25 4:57 ` Al Boldi
2006-07-19 17:02 Chuck Ebbert
2006-07-20 17:23 ` Al Boldi
2006-07-24 15:57 ` Al Boldi
2006-07-16 3:58 Chuck Ebbert
2006-07-16 19:49 ` Al Boldi
2006-07-11 15:22 Frank van Maarseveen
2006-07-11 20:11 ` Arjan van de Ven
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