Re: [Qemu-devel] objective benchmark?

["Kazu" <kazoo@r3.dion.ne.jp>]

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Tuesday, May 16, 2006 8:48 PM Lonnie Mendez wrote:

> Kazu wrote:
>
>>If you set /proc/sys/dev/rtc/max-user-freq to 1024 and disable cpuspeed
>>service that is related to SpeedStep/PowerNow! on a host OS, the clock in
>>guest OS works fine.
>>
>>I checked it on i686/x86_64 Linux host.
>>
>   Mind saying how you checked this?  I'm on a pentium-III mobile
> processor and the only way I've seen so far to make qemu + rdtsc behave
> 100% is by disabling ACPI (boot with -noacpi).  If I add a simple printf
> to cpu_calibrate_ticks it doesn't seem fixed to me:
>
> dignome@vaio /prog/qemu-stuff $ qemu -localtime -hda winxp.img -no-acpi
> -kernel-kqemu -soundhw es1370
> ticks_per_sec set as 1126809000
> dignome@vaio /prog/qemu-stuff $ qemu -localtime -hda winxp.img -no-acpi
> -kernel-kqemu -soundhw es1370
> ticks_per_sec set as 17308857
> dignome@vaio /prog/qemu-stuff $ qemu -localtime -hda winxp.img -no-acpi
> -kernel-kqemu -soundhw es1370
> ticks_per_sec set as 103710852
> dignome@vaio /prog/qemu-stuff $ qemu -localtime -hda winxp.img -no-acpi
> -kernel-kqemu -soundhw es1370
> ticks_per_sec set as 15292604
> dignome@vaio /prog/qemu-stuff $ qemu -localtime -hda winxp.img -no-acpi
> -kernel-kqemu -soundhw es1370
> ticks_per_sec set as 96695295
> dignome@vaio /prog/qemu-stuff $ qemu -localtime -hda winxp.img -no-acpi
> -kernel-kqemu -soundhw es1370
> ticks_per_sec set as 1126761234
> dignome@vaio /prog/qemu-stuff $ qemu -localtime -hda winxp.img -no-acpi
> -kernel-kqemu -soundhw es1370
> ticks_per_sec set as 1126762522
> dignome@vaio /prog/qemu-stuff $ qemu -localtime -hda winxp.img -no-acpi
> -kernel-kqemu -soundhw es1370
> ticks_per_sec set as 49791263
>
>   The first entry is with the patch attached called
> 'ticks_from_proc.patch' applied (I've been using this for almost a
> year).  It sets the value ticks_per_sec, which happens to be used by a
> lot of qemu's hardware emulation, using information in /proc/cpuinfo.
> This doesn't fix the time issue as rdtsc is still used every time a
> SIGALRM signal occurs for timing, but at least the guest's emulated
> hardware runs to speed.
>
> dignome@vaio /prog/qemu-cvs/qemu-acpi/qemu $ find . -type f -exec fgrep
> -l 'ticks_per_sec' {} \;
> ./audio/audio.c
> ./audio/noaudio.c
> ./audio/wavaudio.c
> ./monitor.c
> ./vl.c
> ./vl.h
> ./hw/acpi.c
> ./hw/adlib.c
> ./hw/arm_timer.c
> ./hw/cuda.c
> ./hw/fdc.c
> ./hw/i8254.c
> ./hw/i8259.c
> ./hw/ide.c
> ./hw/mc146818rtc.c
> ./hw/mips_r4k.c
> ./hw/ppc.c
> ./hw/sb16.c
> ./hw/sh7750.c
> ./hw/slavio_timer.c
> ./hw/usb-uhci.c
>
>   The second patch adds the printf statement so you can see this for
> yourself.
>

Here is values of ticks_per_sec on Athlon 64 3000+ .
i686 host:
1790803394
1790784284
1790774719
1790798849
1790814225

x86_64 host:
1790764763
1790815837
1790816089
1790803590
1790771017

If I changed usleep(50 * 1000) to ulseep(500 * 1000) in vl.c, it improves.

When cpuspeed service is working in x86_64 host, it becomes:
994896127
994896984
994895713
994897215
994896447

It is because CPU is changed from 1.8GHz to 1GHz. TSC is changed dynamically
while QEMU is working.
I think your results are from mobile Pentium III.
I don't know much but a power management of mobile Pentium III works without
software?

I attached a patch that I modifed from your patch. It can be applied by
patch -p0. I checked it works for Athlon 64 with cpuspeed service (Power
Now!). ticks_per_sec changed dynamically but a clock of win2k guest on
x86_64 Linux host works fine.

If your guest OS is Linux, it is necessary to set clock=pit at guest OS'es
startup. TSC may change.

I hope it works for SpeedStep.

I can't test i686 Linux host because ACPI and cpuspeed doesn't work on my
PC.

I think it is better to detect CPU change signal and calibrate
ticks_per_sec.

Regards,
Kazu



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Index: vl.c
===================================================================
RCS file: /sources/qemu/qemu/vl.c,v
retrieving revision 1.185
diff -u -r1.185 vl.c
--- vl.c	3 May 2006 22:02:44 -0000	1.185
+++ vl.c	17 May 2006 04:19:00 -0000
@@ -627,8 +627,43 @@
     return tv.tv_sec * 1000000LL + tv.tv_usec;
 }
 
+uint64_t get_tps_from_proc()
+{
+    FILE *fp;
+    char buf[30];
+    double cpu_mhz;
+
+    if (!(fp = fopen("/proc/cpuinfo", "r")))
+        return 0;
+
+    /* find wanted line */
+    while (fgets(buf, 30, fp) != NULL)
+        if (!strncmp(buf, "cpu MHz", 7))
+            break;
+
+    /* line not found? */
+    if (feof(fp)) {
+        fclose(fp);
+        return 0;
+    }
+    fclose(fp);
+
+    /* put 'cpu MHz' value into cpu_mhz */
+    if (!sscanf(&buf[9], ": %lf", &cpu_mhz))
+        return 0;
+
+    /* return estimated ticks/sec value */
+    return (uint64_t)(cpu_mhz * 1000000.0);
+}
+
 void cpu_calibrate_ticks(void)
 {
+    if (!(ticks_per_sec = get_tps_from_proc()))
+        fprintf(stderr, "Could not obtain ticks/sec. from /proc/cpuinfo\n \
+                        resorting to regular method (tsc)\n");
+    else /* value obtained, skip below */
+	return;
+
     int64_t usec, ticks;
 
     usec = get_clock();
@@ -4499,6 +4534,8 @@
     tap_win32_poll();
 #endif
 
+    cpu_calibrate_ticks();
+
     if (vm_running) {
         qemu_run_timers(&active_timers[QEMU_TIMER_VIRTUAL], 
                         qemu_get_clock(vm_clock));