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Old 05-24-2007, 02:15 AM   #1
hemanth_v
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why is physical id odd in /proc/cpuinfo


Output of /proc/cpuinfo shows different Physical-id`s (0,0,3,3). what does this mean ?
why it is displaying physical id 3 in next two logical processor.If it is taking slotwise then it should display 1.
 
Old 05-24-2007, 02:49 AM   #2
x_terminat_or_3
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Because you got hyperthreading enabled

With hyperthreading, each physical cpu is presented to the operating system as two separate instances of the same cpu.

Read more about hyperthreading
 
Old 05-25-2007, 10:53 AM   #3
hemanth_v
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ya got it. But now my new doubt is , if i have got 2 cpu`s which are ht enabled. then the second cpu should have the physical-id as 1,1, instead it shows 3 as the physical-id. why is that so ?

If 0,0 is the physical-id for cpu-1, cpu-2 should have the physical-id as 1,1.Isn`t it ?
 
Old 07-05-2007, 06:51 PM   #4
x_terminat_or_3
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Except, kernels don't always include support for more then 2 cpu's. Any extra cpu makes the kernel a little bit bigger in memory. There's no easy way to found out. But if you want, download the kernel sources from your distrubution and kernel version and variant, then do a make config, and tell it to use the existing .config file, then peruse the options until you get to the one that defines how many cpu's are supported. Tedious at best, and as long as you don't do a make followed by a make install, there is no risk of messing up your system in any way, except to take up 200+MB of disk space.
 
Old 07-05-2007, 08:04 PM   #5
syg00
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Much easier to just {z}grep the config they shipped for NR_CPUS - have a look for a config file in /boot (typically) or /proc/config.gz
 
  


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