On Wed, 2006-11-08 at 15:11 -0800, Tim Chen wrote:
> On Wed, 2006-11-08 at 17:22 +0100, Adrian Bunk wrote:
>
> > There's perhaps one thing that might help us to see whether it's just a
> > benchmark effekt or a real problem:
> >
> > With Tim's CONFIG_NR_CPUS=8, NR_IRQS only increases from 224 in 2.6.18
> > to 512 in 2.6.19-rc.
> >
> > With CONFIG_NR_CPUS=255, NR_IRQS increases from 224 in 2.6.18
> > to 8416 in 2.6.19-rc.
> >
> > @Tim:
> > Can you try CONFIG_NR_CPUS=255 with both 2.6.18 and 2.6.19-rc5?
> >
>
> With CONFIG_NR_CPUS increased from 8 to 64:
> 2.6.18 see no change in fork time measured.
> 2.6.19-rc5 see a 138% increase in fork time.
>
Lmbench is broken in its fork time measurement.
It includes overhead time when it is pinning processes onto
specific cpu. The actual fork time is not affected by NR_IRQS.
Lmbench calls the following C library function to determine the
number of processors online before it pin the processes:
sysconf(_SC_NPROCESSORS_ONLN);
This function takes the same order of time to run as
fork itself. In addition, runtime of this function
increases with NR_IRQS. This resulted in the change in
time measured.
After hardcoding the number of online processors in lmbench,
the fork time measured now does not change with CONFIG_NR_CPUS
for both 2.6.18 and 2.6.19-rc5. So we can now conclude that
NR_IRQS does not affect fork. We can remove this particular
issue from the known regression.
Tim
-
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/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
