Ruben Kerkhof wrote:
It's even higher these days:
grep NR_CPUS /boot/config-2.6.32-220.13.1.el6.x86_64 CONFIG_NR_CPUS=4096
I'm curious, has anyone measured what the memory overhead is of keeping NR_CPUS at 512? arch/x86/Kconfig says "This is purely to save memory - each supported CPU adds approximately eight kilobytes to the kernel image." If that's true, 512 cpus use 4MB, something I'm willing to live with on my 64bit servers.
On Mon, May 21, 2012 at 12:25 AM, Xose Vazquez Perez xose.vazquez@gmail.com wrote:
Ruben Kerkhof wrote:
It's even higher these days:
grep NR_CPUS /boot/config-2.6.32-220.13.1.el6.x86_64 CONFIG_NR_CPUS=4096
I'm curious, has anyone measured what the memory overhead is of keeping NR_CPUS at 512? arch/x86/Kconfig says "This is purely to save memory - each supported CPU adds approximately eight kilobytes to the kernel image." If that's true, 512 cpus use 4MB, something I'm willing to live with on my 64bit servers.
That's on an ancient kernel. I believe some work has been done to reduce the overhead of cpu masks, see https://lkml.org/lkml/2012/2/15/546 for example.
Regards,
Ruben
On Mon, May 21, 2012 at 1:25 AM, Xose Vazquez Perez xose.vazquez@gmail.com wrote:
Ruben Kerkhof wrote:
It's even higher these days:
grep NR_CPUS /boot/config-2.6.32-220.13.1.el6.x86_64 CONFIG_NR_CPUS=4096
I'm curious, has anyone measured what the memory overhead is of keeping NR_CPUS at 512? arch/x86/Kconfig says "This is purely to save memory - each supported CPU adds approximately eight kilobytes to the kernel image." If that's true, 512 cpus use 4MB, something I'm willing to live with on my 64bit servers.
Keep in mind that this bug is ~5 y/o. The last 5 years seen an explosion in both core count and standard memory size in servers. (While on the other hand, a lot of progress was made to reduce the static allocations tied to NR_CPUS)
- Gilboa
kernel@lists.fedoraproject.org