* (AArch64) NR_CPUS limit
@ 2015-02-04 20:23 Jon Masters
2015-02-05 5:49 ` Tyler Baker
0 siblings, 1 reply; 3+ messages in thread
From: Jon Masters @ 2015-02-04 20:23 UTC (permalink / raw)
To: linux-arm-kernel
Hi Folks,
We're currently patching our kernels with a (much) higher maximum for
NR_CPUS. There are some very large ARM systems coming soon - any
objections to increasing this to something like 1024 or 4096?
(If not I'll send Catalin the trivial patch)
Jon.
^ permalink raw reply [flat|nested] 3+ messages in thread
* (AArch64) NR_CPUS limit
2015-02-04 20:23 (AArch64) NR_CPUS limit Jon Masters
@ 2015-02-05 5:49 ` Tyler Baker
2015-02-05 15:58 ` Mark Rutland
0 siblings, 1 reply; 3+ messages in thread
From: Tyler Baker @ 2015-02-05 5:49 UTC (permalink / raw)
To: linux-arm-kernel
Hi Jon,
On 4 February 2015 at 12:23, Jon Masters <jcm@redhat.com> wrote:
> Hi Folks,
>
> We're currently patching our kernels with a (much) higher maximum for
> NR_CPUS. There are some very large ARM systems coming soon - any
> objections to increasing this to something like 1024 or 4096?
FWIW, I have a few ARMv7 systems complaining about this issue as well.
[ 0.000000] WARNING: CPU: 0 PID: 0 at
../arch/arm/kernel/devtree.c:144 arm_dt_init_cpu_maps+0x118/0x1e8()
[ 0.000000] DT /cpu 9 nodes greater than max cores 8, capping them
[ 0.000000] Modules linked in:
[ 0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted
3.19.0-rc7-00032-g5ee0e962603e #1
[ 0.000000] Hardware name: Hisilicon HiP04 (Flattened Device Tree)
[ 0.000000] [<c0215d94>] (unwind_backtrace) from [<c021165c>]
(show_stack+0x10/0x14)
[ 0.000000] [<c021165c>] (show_stack) from [<c091841c>]
(dump_stack+0x78/0x94)
[ 0.000000] [<c091841c>] (dump_stack) from [<c0247bc8>]
(warn_slowpath_common+0x74/0xb0)
[ 0.000000] [<c0247bc8>] (warn_slowpath_common) from [<c0247c98>]
(warn_slowpath_fmt+0x30/0x40)
[ 0.000000] [<c0247c98>] (warn_slowpath_fmt) from [<c0c624b4>]
(arm_dt_init_cpu_maps+0x118/0x1e8)
[ 0.000000] [<c0c624b4>] (arm_dt_init_cpu_maps) from [<c0c613a8>]
(setup_arch+0x714/0xa98)
[ 0.000000] [<c0c613a8>] (setup_arch) from [<c0c5e940>]
(start_kernel+0x94/0x3d4)
[ 0.000000] [<c0c5e940>] (start_kernel) from [<10208084>] (0x10208084)
[ 0.000000] ---[ end trace cb88537fdc8fa200 ]---
Is there an advantage (other than convenience) to increasing this
default, then say using the nr_cpu[1] kernel parameter?
>
> (If not I'll send Catalin the trivial patch)
>
> Jon.
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel at lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
Cheers,
Tyler
[1] https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/kernel-parameters.txt#n2473
^ permalink raw reply [flat|nested] 3+ messages in thread
* (AArch64) NR_CPUS limit
2015-02-05 5:49 ` Tyler Baker
@ 2015-02-05 15:58 ` Mark Rutland
0 siblings, 0 replies; 3+ messages in thread
From: Mark Rutland @ 2015-02-05 15:58 UTC (permalink / raw)
To: linux-arm-kernel
On Thu, Feb 05, 2015 at 05:49:02AM +0000, Tyler Baker wrote:
> Hi Jon,
>
> On 4 February 2015 at 12:23, Jon Masters <jcm@redhat.com> wrote:
> > Hi Folks,
> >
> > We're currently patching our kernels with a (much) higher maximum for
> > NR_CPUS. There are some very large ARM systems coming soon - any
> > objections to increasing this to something like 1024 or 4096?
There's already a patch out there going for 4096:
http://lists.infradead.org/pipermail/linux-arm-kernel/2015-January/318853.html
That seems large enough to cater for everyone. I see x86_64 will go up
to 8192 CPUs in some configurations, and if anyone wants NR_CPUS parity,
now is the time to speak...
Do we have an idea as to what the memory footprint and/or runtime
performance hit looks like going from NR_CPUS=64 to NR_CPUS=4096? It
would be nice to know if there's a scalability problem anywhere in the
arch code.
We also want defconfig to work on as many systems as possible, and it
would be nice to know whether or not bumping the default is feasible.
> FWIW, I have a few ARMv7 systems complaining about this issue as well.
>
> [ 0.000000] WARNING: CPU: 0 PID: 0 at
> ../arch/arm/kernel/devtree.c:144 arm_dt_init_cpu_maps+0x118/0x1e8()
> [ 0.000000] DT /cpu 9 nodes greater than max cores 8, capping them
> [ 0.000000] Modules linked in:
> [ 0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted
> 3.19.0-rc7-00032-g5ee0e962603e #1
> [ 0.000000] Hardware name: Hisilicon HiP04 (Flattened Device Tree)
> [ 0.000000] [<c0215d94>] (unwind_backtrace) from [<c021165c>]
> (show_stack+0x10/0x14)
> [ 0.000000] [<c021165c>] (show_stack) from [<c091841c>]
> (dump_stack+0x78/0x94)
> [ 0.000000] [<c091841c>] (dump_stack) from [<c0247bc8>]
> (warn_slowpath_common+0x74/0xb0)
> [ 0.000000] [<c0247bc8>] (warn_slowpath_common) from [<c0247c98>]
> (warn_slowpath_fmt+0x30/0x40)
> [ 0.000000] [<c0247c98>] (warn_slowpath_fmt) from [<c0c624b4>]
> (arm_dt_init_cpu_maps+0x118/0x1e8)
> [ 0.000000] [<c0c624b4>] (arm_dt_init_cpu_maps) from [<c0c613a8>]
> (setup_arch+0x714/0xa98)
> [ 0.000000] [<c0c613a8>] (setup_arch) from [<c0c5e940>]
> (start_kernel+0x94/0x3d4)
> [ 0.000000] [<c0c5e940>] (start_kernel) from [<10208084>] (0x10208084)
> [ 0.000000] ---[ end trace cb88537fdc8fa200 ]---
>
> Is there an advantage (other than convenience) to increasing this
> default, then say using the nr_cpu[1] kernel parameter?
NR_CPUS >= nr_cpus due to compile-time allocations relying on NR_CPUS.
You can't allocate more space for these at runtime...
Mark.
^ permalink raw reply [flat|nested] 3+ messages in thread
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2015-02-04 20:23 (AArch64) NR_CPUS limit Jon Masters
2015-02-05 5:49 ` Tyler Baker
2015-02-05 15:58 ` Mark Rutland
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