For slow targets and fast hosts, the emulation may be faster
than the actual hardware, which can be undesirable for various
reasons. Add a run-time option to slow down the emulation
by sleeping in the CPU emulation.
Signed-off-by: Wolfgang Mauerer <wolfgang.maue...@siemens.com>
---
cpus.c | 34 ++++++++++++++++++++++++++++++++++
include/qemu-common.h | 2 ++
qemu-options.hx | 13 +++++++++++++
vl.c | 10 ++++++++++
4 files changed, 59 insertions(+), 0 deletions(-)
diff --git a/cpus.c b/cpus.c
index 4a7782a..41a9e0c 100644
--- a/cpus.c
+++ b/cpus.c
@@ -106,6 +106,11 @@ static QEMUTimer *icount_warp_timer;
static int64_t vm_clock_warp_start;
static int64_t qemu_icount;
+static double slowdown_factor = 0.0;
+#ifndef _WIN32
+static struct timespec slowdown_delay;
+#endif
+
typedef struct TimersState {
int64_t cpu_ticks_prev;
int64_t cpu_ticks_offset;
@@ -385,6 +390,21 @@ void configure_icount(const char *option)
qemu_get_clock_ns(vm_clock) + get_ticks_per_sec() / 10);
}
+void configure_slowdown(const char *option)
+{
+ if (!option) {
+ return;
+ }
+
+ slowdown_factor = strtod(option, NULL)/100.0;
+ /* We cannot provide speedups, obviously */
+ if (slowdown_factor < 0) {
+ slowdown_factor *= -1.0;
+ }
+
+ slowdown_delay.tv_sec = 0;
+}
+
/***********************************************************/
void hw_error(const char *fmt, ...)
{
@@ -1092,6 +1112,7 @@ void vm_stop_force_state(RunState state)
static int tcg_cpu_exec(CPUArchState *env)
{
int ret;
+ int64_t ss, delta;
#ifdef CONFIG_PROFILER
int64_t ti;
#endif
@@ -1112,7 +1133,20 @@ static int tcg_cpu_exec(CPUArchState *env)
env->icount_decr.u16.low = decr;
env->icount_extra = count;
}
+ ss = qemu_get_clock_ns(rt_clock);
+
ret = cpu_exec(env);
+
+ if (slowdown_factor > 0) {
+ delta = qemu_get_clock_ns(rt_clock) - ss;
+ delta *= slowdown_factor;
+#ifdef _WIN32
+ Sleep(delta/1000000l);
+#else
+ slowdown_delay.tv_nsec = delta;
+ nanosleep(&slowdown_delay, NULL);
+#endif
+ }
#ifdef CONFIG_PROFILER
qemu_time += profile_getclock() - ti;
#endif
diff --git a/include/qemu-common.h b/include/qemu-common.h
index ca464bb..652abb9 100644
--- a/include/qemu-common.h
+++ b/include/qemu-common.h
@@ -119,6 +119,8 @@ static inline char *realpath(const char *path, char
*resolved_path)
void configure_icount(const char *option);
extern int use_icount;
+void configure_slowdown(const char *option);
+
/* FIXME: Remove NEED_CPU_H. */
#ifndef NEED_CPU_H
diff --git a/qemu-options.hx b/qemu-options.hx
index 9df0cde..2f6580f 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -2665,6 +2665,19 @@ order cores with complex cache hierarchies. The number
of instructions
executed often has little or no correlation with actual performance.
ETEXI
+DEF("slowdown", HAS_ARG, QEMU_OPTION_slowdown, \
+ "-slowdown s \n" \
+ " Slow down the CPU emulation by (approximately) s"
+ " percent\n", QEMU_ARCH_ALL)
+STEXI
+@item -slowdown [@var{s}]
+@findex -slowdown
+Slow down the virtual CPU by approximately s percent. This makes it
+possible to align the emulated machine's performance roughly with
+the performance of physical entities, but does not provide identical
+performance profiles since the emulation is not cycle accurate.
+ETEXI
+
DEF("watchdog", HAS_ARG, QEMU_OPTION_watchdog, \
"-watchdog i6300esb|ib700\n" \
" enable virtual hardware watchdog [default=none]\n",
diff --git a/vl.c b/vl.c
index 79e5122..624551f 100644
--- a/vl.c
+++ b/vl.c
@@ -2524,6 +2524,7 @@ int main(int argc, char **argv, char **envp)
int i;
int snapshot, linux_boot;
const char *icount_option = NULL;
+ const char *slowdown_option = NULL;
const char *initrd_filename;
const char *kernel_filename, *kernel_cmdline;
char boot_devices[33] = "cad"; /* default to HD->floppy->CD-ROM */
@@ -3402,6 +3403,9 @@ int main(int argc, char **argv, char **envp)
case QEMU_OPTION_icount:
icount_option = optarg;
break;
+ case QEMU_OPTION_slowdown:
+ slowdown_option = optarg;
+ break;
case QEMU_OPTION_incoming:
incoming = optarg;
runstate_set(RUN_STATE_INMIGRATE);
@@ -3765,6 +3769,12 @@ int main(int argc, char **argv, char **envp)
/* clean up network at qemu process termination */
atexit(&net_cleanup);
+ if (slowdown_option && (kvm_enabled() || xen_enabled())) {
+ fprintf(stderr, "-slowdown is not allowed with kvm or xen\n");
+ exit(1);
+ }
+ configure_slowdown(slowdown_option);
+
if (net_init_clients() < 0) {
exit(1);
}
--
1.7.1
