kvm: support -overcommit cpu-pm=on|off
With this flag, kvm allows guest to control host CPU power state. This
increases latency for other processes using same host CPU in an
unpredictable way, but if decreases idle entry/exit times for the
running VCPU, so to use it QEMU needs a hint about whether host CPU is
overcommitted, hence the flag name.
Follow-up patches will expose this capability to guest
(using mwait leaf).
Based on a patch by Wanpeng Li <kernellwp@gmail.com> .
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Message-Id: <20180622192148.178309-2-mst@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/qemu-options.hx b/qemu-options.hx
index 3e45483..81b1e99 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -3325,6 +3325,30 @@
(enabled by default).
ETEXI
+DEF("overcommit", HAS_ARG, QEMU_OPTION_overcommit,
+ "--overcommit [mem-lock=on|off][cpu-pm=on|off]\n"
+ " run qemu with overcommit hints\n"
+ " mem-lock=on|off controls memory lock support (default: off)\n"
+ " cpu-pm=on|off controls cpu power management (default: off)\n",
+ QEMU_ARCH_ALL)
+STEXI
+@item -overcommit mem-lock=on|off
+@item -overcommit cpu-pm=on|off
+@findex -overcommit
+Run qemu with hints about host resource overcommit. The default is
+to assume that host overcommits all resources.
+
+Locking qemu and guest memory can be enabled via @option{mem-lock=on} (disabled
+by default). This works when host memory is not overcommitted and reduces the
+worst-case latency for guest. This is equivalent to @option{realtime}.
+
+Guest ability to manage power state of host cpus (increasing latency for other
+processes on the same host cpu, but decreasing latency for guest) can be
+enabled via @option{cpu-pm=on} (disabled by default). This works best when
+host CPU is not overcommitted. When used, host estimates of CPU cycle and power
+utilization will be incorrect, not taking into account guest idle time.
+ETEXI
+
DEF("gdb", HAS_ARG, QEMU_OPTION_gdb, \
"-gdb dev wait for gdb connection on 'dev'\n", QEMU_ARCH_ALL)
STEXI
