On Fri, 22 Jun 2018 22:22:05 +0300
"Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote:
> 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@xxxxxxxxx> .
>
> Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> ---
> include/sysemu/sysemu.h | 1 +
> target/i386/kvm.c | 23 +++++++++++++++++++++++
> vl.c | 32 +++++++++++++++++++++++++++++++-
> qemu-options.hx | 27 +++++++++++++++++++++++++--
> 4 files changed, 80 insertions(+), 3 deletions(-)
>
> diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
> index e893f72f3b..b921c6f3b7 100644
> --- a/include/sysemu/sysemu.h
> +++ b/include/sysemu/sysemu.h
> @@ -128,6 +128,7 @@ extern bool boot_strict;
> extern uint8_t *boot_splash_filedata;
> extern size_t boot_splash_filedata_size;
> extern bool enable_mlock;
> +extern bool enable_cpu_pm;
> extern uint8_t qemu_extra_params_fw[2];
> extern QEMUClockType rtc_clock;
> extern const char *mem_path;
> diff --git a/target/i386/kvm.c b/target/i386/kvm.c
> index 44f70733e7..cf9107be4b 100644
> --- a/target/i386/kvm.c
> +++ b/target/i386/kvm.c
> @@ -1357,6 +1357,29 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
> smram_machine_done.notify = register_smram_listener;
> qemu_add_machine_init_done_notifier(&smram_machine_done);
> }
> +
> + if (enable_cpu_pm) {
> + int disable_exits = kvm_check_extension(s, KVM_CAP_X86_DISABLE_EXITS);
> + int ret;
> +
> +/* Work around for kernel header with a typo. TODO: fix header and drop. */
> +#if defined(KVM_X86_DISABLE_EXITS_HTL) && !defined(KVM_X86_DISABLE_EXITS_HLT)
> +#define KVM_X86_DISABLE_EXITS_HLT KVM_X86_DISABLE_EXITS_HTL
> +#endif
> + if (disable_exits) {
> + disable_exits &= (KVM_X86_DISABLE_EXITS_MWAIT |
> + KVM_X86_DISABLE_EXITS_HLT |
> + KVM_X86_DISABLE_EXITS_PAUSE);
> + }
> +
> + ret = kvm_vm_enable_cap(s, KVM_CAP_X86_DISABLE_EXITS, 0,
> + disable_exits);
> + if (ret < 0) {
> + error_report("kvm: guest stopping CPU not supported: %s",
> + strerror(-ret));
> + }
> + }
> +
> return 0;
> }
>
> diff --git a/vl.c b/vl.c
> index 06031715ac..c9530efed5 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -142,6 +142,7 @@ ram_addr_t ram_size;
> const char *mem_path = NULL;
> int mem_prealloc = 0; /* force preallocation of physical target memory */
> bool enable_mlock = false;
> +bool enable_cpu_pm = false;
> int nb_nics;
> NICInfo nd_table[MAX_NICS];
> int autostart;
> @@ -390,6 +391,22 @@ static QemuOptsList qemu_realtime_opts = {
> },
> };
>
> +static QemuOptsList qemu_overcommit_opts = {
> + .name = "overcommit",
> + .head = QTAILQ_HEAD_INITIALIZER(qemu_overcommit_opts.head),
> + .desc = {
> + {
> + .name = "mem-lock",
> + .type = QEMU_OPT_BOOL,
> + },
> + {
> + .name = "cpu-pm",
> + .type = QEMU_OPT_BOOL,
> + },
> + { /* end of list */ }
> + },
> +};
> +
> static QemuOptsList qemu_msg_opts = {
> .name = "msg",
> .head = QTAILQ_HEAD_INITIALIZER(qemu_msg_opts.head),
> @@ -3903,7 +3920,20 @@ int main(int argc, char **argv, char **envp)
> if (!opts) {
> exit(1);
> }
> - enable_mlock = qemu_opt_get_bool(opts, "mlock", true);
> + /* Don't override the -overcommit option if set */
> + enable_mlock = enable_mlock ||
> + qemu_opt_get_bool(opts, "mlock", true);
> + break;
> + case QEMU_OPTION_overcommit:
> + opts = qemu_opts_parse_noisily(qemu_find_opts("overcommit"),
> + optarg, false);
> + if (!opts) {
> + exit(1);
> + }
> + /* Don't override the -realtime option if set */
> + enable_mlock = enable_mlock ||
> + qemu_opt_get_bool(opts, "mem-lock", false);
> + enable_cpu_pm = qemu_opt_get_bool(opts, "cpu-pm", false);
should we error out or complain if the option can't be used
/i.e. in case of non kvm accelerator/
instead of silently ignoring it and making user wonder why it doesn't work?
> break;
> case QEMU_OPTION_msg:
> opts = qemu_opts_parse_noisily(qemu_find_opts("msg"), optarg,
> diff --git a/qemu-options.hx b/qemu-options.hx
> index c0d3951e9f..1bba3d258b 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -3328,8 +3328,7 @@ DEF("realtime", HAS_ARG, QEMU_OPTION_realtime,
> "-realtime [mlock=on|off]\n"
> " run qemu with realtime features\n"
> " mlock=on|off controls mlock support (default: on)\n",
> - QEMU_ARCH_ALL)
> -STEXI
> + QEMU_ARCH_ALL) STEXI
> @item -realtime mlock=on|off
> @findex -realtime
> Run qemu with realtime features.
> @@ -3337,6 +3336,30 @@ 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
