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* [Qemu-devel] [PATCH] Add option to slow down qemu
@ 2013-01-11 13:40 Wolfgang Mauerer
  2013-01-11 19:58 ` Stefan Weil
  0 siblings, 1 reply; 10+ messages in thread
From: Wolfgang Mauerer @ 2013-01-11 13:40 UTC (permalink / raw)
  To: qemu-devel, aliguori

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.mauerer@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

^ permalink raw reply related	[flat|nested] 10+ messages in thread
end of thread, other threads:[~2013-05-07 11:26 UTC | newest]

Thread overview: 10+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2013-01-11 13:40 [Qemu-devel] [PATCH] Add option to slow down qemu Wolfgang Mauerer
2013-01-11 19:58 ` Stefan Weil
2013-01-17 17:10   ` [Qemu-devel] [[PATCH v2]] Add option to slow qemu down Wolfgang Mauerer
2013-01-17 20:21     ` Stefan Weil
2013-01-18 12:04       ` Wolfgang Mauerer
2013-01-18 12:05       ` [Qemu-devel] [PATCH] " Wolfgang Mauerer
2013-05-07  9:12       ` [Qemu-devel] [[PATCH v2]] " Wolfgang Mauerer
2013-05-07 10:56         ` Markus Armbruster
2013-05-07 11:30           ` Wolfgang Mauerer
2013-01-17 17:14   ` [Qemu-devel] [PATCH] Add option to slow down qemu Wolfgang Mauerer

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