softclock swis not bound to specific cpu

Ivan Voras ivoras at
Mon Oct 19 15:20:06 UTC 2009

Ivan Voras wrote:
> Robert Watson wrote:
>> On Sun, 18 Oct 2009, Taku YAMAMOTO wrote:
>>> I noticed that the softclock threads didn't seem to be bound to any cpu.
>>> I'm not sure whether it's the Right Thing (TM) to bind them to the 
>>> corresponding cpus though: it might be good to give the scheduler a 
>>> chance to rebalance callouts.
>>> I'm about to test the modification like the attached diff. Comments 
>>> are welcome.
>> Yes, I think the intent is that they have a "soft" affinity to the CPU 
>> where the lapic timer is firing, but not a hard binding, allowing them 
>> to migrate if required.  It would be interesting to measure how 
>> effective that soft affinity is in practice under various loads -- 
>> presumably the goal would be for the softclock thread to migrate if a 
>> higher (lower) priority thread is hogging the CPU.
> So why are there NCPU softclock threads if the binding isn't important?

Nevermind, I got it - they are not used only for "clock".

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