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author | jhb <jhb@FreeBSD.org> | 2004-07-02 20:21:44 +0000 |
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committer | jhb <jhb@FreeBSD.org> | 2004-07-02 20:21:44 +0000 |
commit | 696704716d52a895094da20b7e1a0f763b069e12 (patch) | |
tree | 2a5d6a91ba98f5b9e075eecc1a9ca724b8a9110a /share/mk/bsd.port.subdir.mk | |
parent | 1f506bc6fab7cc97cb923d4af1174f9c732221dd (diff) | |
download | FreeBSD-src-696704716d52a895094da20b7e1a0f763b069e12.zip FreeBSD-src-696704716d52a895094da20b7e1a0f763b069e12.tar.gz |
Implement preemption of kernel threads natively in the scheduler rather
than as one-off hacks in various other parts of the kernel:
- Add a function maybe_preempt() that is called from sched_add() to
determine if a thread about to be added to a run queue should be
preempted to directly. If it is not safe to preempt or if the new
thread does not have a high enough priority, then the function returns
false and sched_add() adds the thread to the run queue. If the thread
should be preempted to but the current thread is in a nested critical
section, then the flag TDF_OWEPREEMPT is set and the thread is added
to the run queue. Otherwise, mi_switch() is called immediately and the
thread is never added to the run queue since it is switch to directly.
When exiting an outermost critical section, if TDF_OWEPREEMPT is set,
then clear it and call mi_switch() to perform the deferred preemption.
- Remove explicit preemption from ithread_schedule() as calling
setrunqueue() now does all the correct work. This also removes the
do_switch argument from ithread_schedule().
- Do not use the manual preemption code in mtx_unlock if the architecture
supports native preemption.
- Don't call mi_switch() in a loop during shutdown to give ithreads a
chance to run if the architecture supports native preemption since
the ithreads will just preempt DELAY().
- Don't call mi_switch() from the page zeroing idle thread for
architectures that support native preemption as it is unnecessary.
- Native preemption is enabled on the same archs that supported ithread
preemption, namely alpha, i386, and amd64.
This change should largely be a NOP for the default case as committed
except that we will do fewer context switches in a few cases and will
avoid the run queues completely when preempting.
Approved by: scottl (with his re@ hat)
Diffstat (limited to 'share/mk/bsd.port.subdir.mk')
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