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author | Marcelo Tosatti <mtosatti@redhat.com> | 2015-04-08 20:33:24 -0300 |
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committer | Anders Roxell <anders.roxell@linaro.org> | 2015-08-17 08:59:43 +0200 |
commit | e64e9fa132c60709e6f75da4279adebe59d3f66b (patch) | |
tree | 0e9313162dbd65bea8b32f452a46c0fe16c8eb7e /arch/powerpc/include/asm/dcr-generic.h | |
parent | ae86169aa58855dc944b1e1a21bd7f12bbbf90f9 (diff) |
KVM: use simple waitqueue for vcpu->wq
The problem:
On -RT, an emulated LAPIC timer instances has the following path:
1) hard interrupt
2) ksoftirqd is scheduled
3) ksoftirqd wakes up vcpu thread
4) vcpu thread is scheduled
This extra context switch introduces unnecessary latency in the
LAPIC path for a KVM guest.
The solution:
Allow waking up vcpu thread from hardirq context,
thus avoiding the need for ksoftirqd to be scheduled.
Normal waitqueues make use of spinlocks, which on -RT
are sleepable locks. Therefore, waking up a waitqueue
waiter involves locking a sleeping lock, which
is not allowed from hard interrupt context.
cyclictest command line:
# cyclictest -m -n -q -p99 -l 1000000 -h60 -D 1m
This patch reduces the average latency in my tests from 14us to 11us.
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Diffstat (limited to 'arch/powerpc/include/asm/dcr-generic.h')
0 files changed, 0 insertions, 0 deletions