to scale more gracefully when there are thousands of active threads.
Proposed on tech-kern@.
- Use LOCKDEBUG to catch some errors in the use of condition variables:
freeing an active CV
re-initializing an active CV
using multiple distinct mutexes during concurrent waits
not holding the interlocking mutex when calling cv_broadcast/cv_signal
waking waiters and destroying the CV before they run and exit it
- Tweak it so it can also catch common errors with condition variables.
The change to kern_condvar.c is not included in this commit and will
come later.
- Don't call kmem_alloc() if operating in interrupt context, just fail
the allocation and disable debugging for the object. Makes it safe
to do mutex_init/rw_init/cv_init in interrupt context, when running
a LOCKDEBUG kernel.
* NOTE: if you get a panic in this code block, it is likely that
* a lock has been destroyed or corrupted while still in use. Try
* compiling a kernel with LOCKDEBUG to pinpoint the problem.
mi_switch(), migration for LSONPROC is now performed via idle loop.
Handles/fixes on-CPU case in lwp_migrate(), misc.
Closes PR/38169, idea of migration via idle loop by Andrew Doran.
NetBSD's shutdown behavior of more than 6 years before rev 1.176.
Ok joerg@.
It is essential that we restore some hardware to initial conditions
before rebooting, in order to avoid interfering with the BIOS
bootstrap. For example, if NetBSD gives control back to the Soekris
comBIOS while the kernel text is write-protected, the BIOS bootstrap
hangs during the power-on self-test, "POST: 0123456789bcefghip".
In principle, bus masters can also interfere with BIOS boot.
- Fix performance regression inroduced by the workaround by making job
stealing a lot simpler: if the local run queue is empty, let the CPU enter
the idle loop. In the idle loop, try to steal a job from another CPU's run
queue if we are idle. If we succeed, re-enter mi_switch() immediatley to
dispatch the job.
- When stealing jobs, consider a remote CPU to have one less job in its
queue if it's currently in the idle loop. It will dispatch the job soon,
so there's no point sloshing it about.
- Introduce a few event counters to monitor what's happening with the run
queues.
- Revert the idle CPU bitmap change. It's pointless considering NUMA.
