Re: How to change the number of processors in a 16-core machine

2007-11-12 Thread Bill Rugolsky Jr. 
On Mon, Nov 12, 2007 at 09:48:41AM +, Rui Tiago Matos wrote:
 On 12/11/2007, Feng Xian [EMAIL PROTECTED] wrote:
  Hi,
 
   I am doing a scalable test on a 16-core machine (8 dual-core amd
  processors). So I need to vary the processors from 1 to 16. But I
  couldnt remove the cores from motherboard. Is there any way to achieve
  this by changing the max number of processors in the kernel? Thanks!
 
 From Documentation/kernel-parameters.txt in a linux source tree:
 
 maxcpus=[SMP] Maximum number of processors that an SMP kernel
 should make use of.  maxcpus=n : n = 0 limits the
 kernel to using 'n' processors.  n=0 is a special 
 case,
 it is equivalent to nosmp, which also disables
 the IO APIC.
 
 Just add that parameter on your grub config or directly on the grub shell.

With CPU hotplug, you don't even have to reboot.
See  Documentation/cpu-hotplug.txt:

...

Command Line Switches
-
maxcpus=nRestrict boot time cpus to n. Say if you have 4 cpus, using
 maxcpus=2 will only boot 2. You can choose to bring the
 other cpus later online, read FAQ's for more info.

additional_cpus=n (*)   Use this to limit hotpluggable cpus. This option sets
cpu_possible_map = cpu_present_map + additional_cpus


...

Q: How do i logically offline a CPU?
A: Do the following.

#echo 0  /sys/devices/system/cpu/cpuX/online


[echo 1 into the same file to bring it back online.]

Regards,

Bill Rugolsky

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Re: How to change the number of processors in a 16-core machine

2007-11-12 Thread Bill Rugolsky Jr. 
On Mon, Nov 12, 2007 at 09:52:49AM -0500, Bill Rugolsky Jr. wrote:
 With CPU hotplug, you don't even have to reboot.

One additional note: Since the Opteron boxes are NUMA, the memory topology
(and any differences from the online CPU topology) may also affect your
performance benchmark results.

-Bill

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Re: help! My re-compiled kernel always got crashed in a machine with scsi/sata disk

2007-11-12 Thread Jarod Wilson 
Feng Xian wrote:
 I downloaded a clean version of 2.6.23 and didnt do any modification on
 it (athough I am about to modify it in the future). By default, the
 clean version doesnt enable sata features, so I enabled these features
 and compiled this clean version. But I couldn't boot linux with the
 compiled kernel like I mentioned in my previous posts.

Like I said, its not a Fedora kernel, and thus not something we can
reasonably support here. The only possible list-relevant bit of info
here would be knowing *why* you're building your own, such that we can
make the Fedora kernel provide what you need so you don't have to, if
possible and/or relevant.

That said, seeing as how a Fedora kernel does boot your system, you'll
probably get a lot closer to a bootable system with your own kernel if
you start with the Fedora kernel config file instead of the upstream
kernel config file, and go from there.


 On 11/12/07, *Jarod Wilson* [EMAIL PROTECTED]
 mailto:[EMAIL PROTECTED] wrote:
 
 Feng Xian wrote:
  Thanks for all your help. I ran into another problem.
 
  My 16-core machine has a scsi/sata disk. I have enabled all important
  features related with scsi and sata.  I built 2.6.23 kernel on this
  machine. But the kernel always got crashed randomly. Sometimes it
  couldnot even boot, reporting some random errors,  like segment
  violation, sleep for 40 seconds, or Group volume VolGroup00 uses
 lvm2
  metadata: read-only, then jump to a strange login window that I
 cannot
  log in using my root password.
 
   Another thing is that Linux works perfect if I installed Fecore
 Core 7
  on this multi-core machine with scsi/sata disk. Why it didnt work if I
  used re-compiled kernel. I guess it is because I didnt config kernel
  right (although I enabled all important features related with
 scsi/sata)
  in make menuconfig. If you happen to know how to enable scsi/sata
  features correctly, please let me know. Thanks!
 
 I don't think this is the correct forum for this question. This list is
 targeted at issues surrounding the Fedora kernel, and you're building
 your own kernel. Once you start building your own, with a config that
 obviously differs significantly from the Fedora config, we can't
 realistically provide support here.
 
 Furthermore, I'm not quite sure I understand why you think you need to
 build your own kernel either. To be bluntly honest, if you can't figure
 out what's going wrong there on your own, you probably shouldn't be
 building your own.


-- 
Jarod Wilson
[EMAIL PROTECTED]




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