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kvm: support -overcommit cpu-pm=on|off

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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>
This commit is contained in:
Michael S. Tsirkin 2018-06-22 22:22:05 +03:00 • committed by Paolo Bonzini
parent 0c8465440d
commit 6f131f13e6
4 changed files with 79 additions and 1 deletions
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24
qemu-options.hx
View file

@ -3325,6 +3325,30 @@ mlocking qemu and guest memory can be enabled via @option{mlock=on}
(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