On Thu, Oct 24, 2019 at 09:41:22AM -0500, Jeremy Linton wrote:
Hi,
On 8/22/19 11:36 AM, Laura Abbott wrote:
> On 8/22/19 8:58 AM, Prarit Bhargava wrote:
> > On 8/19/19 9:15 AM, Laura Abbott wrote:
> > > On 8/16/19 2:57 PM, Paul Bolle wrote:
> > > > Florian Weimer schreef op vr 16-08-2019 om 14:04 [+0200]:
> > > > > RHEL has a larger NR_CPU value, though. For example, it's
8192 on
> > > > > x86-64, while Fedora 31 has 1024.
> > > >
> > > > On the Fedora x86-64 debug builds it's 8192 again. Why's
that?
> > > >
> > > >
> > > > Paul Bolle
> > > >
> > >
> > > That's the option for max cpus. We don't want to turn it on in
all
> > > Fedora builds since it would use up more resources we probably don't
> > > actually need. Turning on for debugging in Fedora is okay though.
> > > RHEL is focused on larger footprints and makes the trade off to
> > > have it enabled all the time.
> > >
> >
> > I think I measured the impact of 8192 vs 512 (or 256?) a long time
> > ago and we
> > are talking about _k_ of memory. We should stick with what upstream
> > has at
> > 8192. It's easier to debug when we have the same value as the
> > default IMO.
> >
> > Having said that, it has been a long time since I had to debug a
> > NR_CPUS/nr_cpus
> > issue in the kernel. We're just not seeing bugs around the value
> > anymore.
> >
>
> I was going to ask about the actual impact of a larger number of CPUs.
> If it's
> actually only k of memory it's probably better to just set MAXCPUS all
> the time.
> Even the lowest end machines probably see more change when frameworks
> change.
>
> And yes, I also think that we've come a long way so NR_CPUS is less of
> an important
> option to optimize these days. I think I'll just submit another patch to
> just do
> the max cpus.
>
Forgive me if you have already posted (didn't see it yet).
Its probably a good idea to bump the aarch64 config at the same time. Some
aarch64 "desktop" machines is already at the 256 core limit currently in
use.
I've bumped aarch64 up to 4096, s390x up to 512, and powerpc up to 2048
in Rawhide and it'll be in the build after v5.4-rc6.
- Jeremy