svn commit: r211176 - in head/sys: amd64/amd64 i386/i386
jhb at FreeBSD.org
Wed Aug 11 17:42:45 UTC 2010
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
>>> 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.
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