RE: kernel optimization
On Wed, 2005-07-27 at 06:53 +0300, Al Boldi wrote: > Gettimeofday loops using gcc-3.2.2 on 2.4.31 and 2.6.12. > > Also, 2.4 is faster than 2.6! All this proves is that gettimeofday() is faster on 2.4 than 2.6. Hardly surprising. Lee - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
RE: kernel optimization
Adrian Bunk wrote: {
On Tue, Jul 26, 2005 at 08:22:59AM +0300, Al Boldi wrote:
> Dr. Horst H. von Brand wrote: {
> Al Boldi <[EMAIL PROTECTED]> wrote:
> > Adrian Bunk wrote: {
> > On Fri, Jul 22, 2005 at 07:55:48PM +0100, christos gentsis wrote:
> > > i would like to ask if it possible to change the optimization of the
> > > kernel from -O2 to -O3 :D, how can i do that? if i change it to the
> > > top level Makefile does it change to all the Makefiles?
> > And since it's larger, it's also slower.
> > }
>
> > It's faster but it's flawed. Root-NFS boot failed!
>
> How do you know that it is faster if it is busted?
> }
>
> The -O3 compile produces a faster kernel, which seems to work perfectly,
> albeit the Root-NFS boot flaw!
How did you measure that you that your -O3 kernel isn't slower?
}
Gettimeofday loops using gcc-3.2.2 on 2.4.31 and 2.6.12.
Also, 2.4 is faster than 2.6!
Try this:
#define __USE_GNU
#include
#include
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);
}
int main(int argc, char *argv[]) {
int i;
elapsed(1);
for (i = 0; elapsed(0) < 100; i++) {
int ret = i;
if (ret > i)
break;
else if (ret < 0) {
perror("not here");
break;
}
ret++;
}
printf("Elapsed: %lu in %lums %lu/ms",i,elapsed(0),i/elapsed(0));
int tmo=i;
elapsed(1);
for (i = 0; i < 100*tmo ; i++) {
int ret = i;
if (ret > i)
break;
else if (ret < 0) {
perror("not here");
break;
}
ret++;
}
printf(" - %lu/ms",i/elapsed(0));
elapsed(1);
for (i = 0; i < 100*tmo ; i++);
printf(" - %lu/ms\n",i/elapsed(0));
return 0;
}
--
Al
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Re: kernel optimization
On Tue, Jul 26, 2005 at 08:22:59AM +0300, Al Boldi wrote:
> Dr. Horst H. von Brand wrote: {
> Al Boldi <[EMAIL PROTECTED]> wrote:
> > Adrian Bunk wrote: {
> > On Fri, Jul 22, 2005 at 07:55:48PM +0100, christos gentsis wrote:
> > > i would like to ask if it possible to change the optimization of the
> > > kernel from -O2 to -O3 :D, how can i do that? if i change it to the
> > > top level Makefile does it change to all the Makefiles?
> > And since it's larger, it's also slower.
> > }
>
> > It's faster but it's flawed. Root-NFS boot failed!
>
> How do you know that it is faster if it is busted?
> }
>
> The -O3 compile produces a faster kernel, which seems to work perfectly,
> albeit the Root-NFS boot flaw!
How did you measure that you that your -O3 kernel isn't slower?
> Al
cu
Adrian
--
"Is there not promise of rain?" Ling Tan asked suddenly out
of the darkness. There had been need of rain for many days.
"Only a promise," Lao Er said.
Pearl S. Buck - Dragon Seed
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RE: kernel optimization
Dr. Horst H. von Brand wrote: {
Al Boldi <[EMAIL PROTECTED]> wrote:
> Adrian Bunk wrote: {
> On Fri, Jul 22, 2005 at 07:55:48PM +0100, christos gentsis wrote:
> > i would like to ask if it possible to change the optimization of the
> > kernel from -O2 to -O3 :D, how can i do that? if i change it to the
> > top level Makefile does it change to all the Makefiles?
> And since it's larger, it's also slower.
> }
> It's faster but it's flawed. Root-NFS boot failed!
How do you know that it is faster if it is busted?
}
The -O3 compile produces a faster kernel, which seems to work perfectly,
albeit the Root-NFS boot flaw!
--
Al
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Re: kernel optimization
I submit that sparse switch jump table's are not an "unusual" construct in the Linux kernel/drivers. GCC only creates a table large enough to cover the largest of the sparse values - it doesn't have to be 0...255. 0...60 with 10 values sparsely scattered would generate a 61 element jump table. There's many K of locked memory in these sparse jump tables. About 2K worth in the VT102 code alone. - Original Message - From: "Alan Cox" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Cc: "Adrian Bunk" <[EMAIL PROTECTED]>; Sent: Saturday, July 23, 2005 15:50 Subject: Re: kernel optimization > On Sad, 2005-07-23 at 02:30 -0400, [EMAIL PROTECTED] wrote: > > Larger does not always mean slower. If it did, nobody would implement a > > loop unrolling optimization. > > Generally speaking nowdays it does. Almost all loop unrolls are a loss > on PIV. > > > ex. Look at how GCC generates jump tables for switch() when there's about > > 10-12 (or more) case's sparsely scattered in the rage from 0 through 255. > > You are comparing with very expensive jump operations its an unusual > case. For the majority of situations the TLB/cache overhead of misses > vastly outweighs the odd clock cycle gained by verbose output. > > - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: kernel optimization
On Sad, 2005-07-23 at 02:30 -0400, [EMAIL PROTECTED] wrote: > Larger does not always mean slower. If it did, nobody would implement a > loop unrolling optimization. Generally speaking nowdays it does. Almost all loop unrolls are a loss on PIV. > ex. Look at how GCC generates jump tables for switch() when there's about > 10-12 (or more) case's sparsely scattered in the rage from 0 through 255. You are comparing with very expensive jump operations its an unusual case. For the majority of situations the TLB/cache overhead of misses vastly outweighs the odd clock cycle gained by verbose output. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: kernel optimization
christos gentsis skrev: so if i want to play with and see what happens i have to change it manually in each make file... good i may create a kernel like that to see what will happens (just for test) ;) thanks Chris Just edit the top level Makefile and add your custom CFLAGS there. But you are risking the stability of your system and don't expect it to be faster. -- Simon Strandman <[EMAIL PROTECTED]> - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: kernel optimization
- Original Message - From: "Adrian Bunk" <[EMAIL PROTECTED]> To: "christos gentsis" <[EMAIL PROTECTED]> Cc: Sent: Friday, July 22, 2005 16:14 Subject: Re: kernel optimization > > It's completely untested. > And since it's larger, it's also slower. Larger does not always mean slower. If it did, nobody would implement a loop unrolling optimization. ex. Look at how GCC generates jump tables for switch() when there's about 10-12 (or more) case's sparsely scattered in the rage from 0 through 255. It generates a 256 element directly indexed jump table (obviously with many duplicate entries). This is faster than a cascaded if/else construct(particularly for those that would have been on the end of the if/else chain), but it is a very large construct. You'll see some of these "plump" switches generated in various SCSI drivers and in the VT102 emulation if you disassemble them. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
RE: kernel optimization
Adrian Bunk wrote: {
On Fri, Jul 22, 2005 at 07:55:48PM +0100, christos gentsis wrote:
> i would like to ask if it possible to change the optimization of the
> kernel from -O2 to -O3 :D, how can i do that? if i change it to the
> top level Makefile does it change to all the Makefiles?
And since it's larger, it's also slower.
}
It's faster but it's flawed. Root-NFS boot failed!
-
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Please read the FAQ at http://www.tux.org/lkml/
Re: kernel optimization
Adrian Bunk wrote: On Fri, Jul 22, 2005 at 07:55:48PM +0100, christos gentsis wrote: hello Hi Chris, i would like to ask if it possible to change the optimization of the kernel from -O2 to -O3 :D, how can i do that? if i change it to the top level Makefile does it change to all the Makefiles? search for the line with CFLAGS += -O2 and change this to -O3. This works for most Makefile's except for the one's that manually set -Os. And let's say that i change it... does this generate any problems with the space that the kernel will take? (the kernel will be much larger) It's completely untested. And since it's larger, it's also slower. Thanks Chris cu Adrian so if i want to play with and see what happens i have to change it manually in each make file... good i may create a kernel like that to see what will happens (just for test) ;) thanks Chris - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: kernel optimization
On Fri, Jul 22, 2005 at 12:52:22PM -0700, David Lang wrote: > This is a airly frequent question > > the short answer is 'don't try' > > the longer answer is that all the additional optimization options that are > part of O3+ are considered individually and if they make sense for the > kernel they are explicitly enabled (in some cases the optimizations need > to be explicitly turned off for proper functionality of the kernel under > all versions of GCC) As far as I can see, none of the additional optimizations with -O3 is enabled in the kernel. > David Lang cu Adrian -- "Is there not promise of rain?" Ling Tan asked suddenly out of the darkness. There had been need of rain for many days. "Only a promise," Lao Er said. Pearl S. Buck - Dragon Seed - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: kernel optimization
On Fri, Jul 22, 2005 at 07:55:48PM +0100, christos gentsis wrote: > hello Hi Chris, > i would like to ask if it possible to change the optimization of the > kernel from -O2 to -O3 :D, how can i do that? if i change it to the top > level Makefile does it change to all the Makefiles? search for the line with CFLAGS += -O2 and change this to -O3. This works for most Makefile's except for the one's that manually set -Os. > And let's say that i change it... does this generate any problems with > the space that the kernel will take? (the kernel will be much larger) It's completely untested. And since it's larger, it's also slower. > Thanks > Chris cu Adrian -- "Is there not promise of rain?" Ling Tan asked suddenly out of the darkness. There had been need of rain for many days. "Only a promise," Lao Er said. Pearl S. Buck - Dragon Seed - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: kernel optimization
This is a airly frequent question the short answer is 'don't try' the longer answer is that all the additional optimization options that are part of O3+ are considered individually and if they make sense for the kernel they are explicitly enabled (in some cases the optimizations need to be explicitly turned off for proper functionality of the kernel under all versions of GCC) David Lang On Fri, 22 Jul 2005, christos gentsis wrote: Date: Fri, 22 Jul 2005 19:55:48 +0100 From: christos gentsis <[EMAIL PROTECTED]> To: linux-kernel@vger.kernel.org Subject: kernel optimization hello i would like to ask if it possible to change the optimization of the kernel from -O2 to -O3 :D, how can i do that? if i change it to the top level Makefile does it change to all the Makefiles? And let's say that i change it... does this generate any problems with the space that the kernel will take? (the kernel will be much larger) Thanks Chris - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ -- There are two ways of constructing a software design. One way is to make it so simple that there are obviously no deficiencies. And the other way is to make it so complicated that there are no obvious deficiencies. -- C.A.R. Hoare - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
