svn commit: r211176 - in head/sys: amd64/amd64 i386/i386

[John Baldwin]

Attilio Rao wrote:
> 2010/8/11 John Baldwin <jhb at freebsd.org>:
>> Attilio Rao wrote:
>>> Author: attilio
>>> Date: Wed Aug 11 10:51:27 2010
>>> New Revision: 211176
>>> URL: http://svn.freebsd.org/changeset/base/211176
>>>
>>> Log:
>>>  IPI handlers may run generally with interrupts disabled because they
>>>  are served via an interrupt gate.
>>>    However, that doesn't explicitly prevent preemption and thread
>>>  migration thus scheduler pinning may be necessary in some handlers.
>>>  Fix that.
>>>    Tested by:  gianni
>>>  MFC after:    1 month
>> Actually that does prevent preemption if you do not call any code that would
>> schedule a thread.  I think this change is all safe to revert.
> 
> Do you recall, then, why lapic_handle_timer() does critical section?
> It seems to be catered by interrupt gate as well, and I don't see any
> point re-enabling them explicitly.

Because hardclock() explicitly calls sched_add() via swi_sched() when 
scheduling the softclock swi.  The critical section there is just to 
ensure that the preemption to softclock happens after all of the clock 
interrupt handlers have finished.  However, PCPU_GET() does not call 
sched_add(), so it does not need to be protected.

-- 
John Baldwin