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Re: maximum number of CPUs
On 25 February 2012 15:22, Christoph Egger <Christoph_Egger%gmx.de@localhost>
> On 25.02.12 10:29, Sad Clouds wrote:
>> On Thu, 23 Feb 2012 20:58:45 +0000
>> Mindaugas Rasiukevicius <rmind%netbsd.org@localhost> wrote:
>>> Brook Milligan <brook%nmsu.edu@localhost> wrote:
>>>> I understand that at least on the i386/amd64 ports CPUs are tracked
>>>> with a 32-bit mask and thus at most 32 CPUs may be active. How
>>>> complex is the task of removing this limitation so that a larger
>>>> number of CPUs may be used?
>>> I have a preliminary patch to support up to 255 CPUs on amd64 (not
>>> worth on i386), however there is still some bug in the early
>>> initialisation code, when TLBs are not being flushed. I have not had
>>> time yet to debug it out.
>>> Apart from that bug, it should be mostly complete.
>> Why limit this to 255?
> This is the limit on x86. The LAPIC field is just 8bit wide.
> On other platforms this patch can add support for a lot more cpus.
>> There are systems out there that surpass this
>> number. I developed some code that uses a 64 element array of 64-bit
>> integers to give 64 * 64 = 4096 bits, which can be used to tracking
>> boolean on/off states.
>> If people are interested in using this for tracking CPU states, I can
>> provide the source code under BSD license.
mrg@ pointed out offline that the x2apic has a 32bit xapic id field...
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