Re: kvm very slow

Luca Tettamanti
2007-08-07T20:49:22Z

Il Tue, Aug 07, 2007 at 02:08:08PM +0200, Luca ha scritto:
> On 8/7/07, Dor Laor <dor.laor-atKUWr5tajBWk0Htik3J/w@public.gmane.org> wrote:
> > Luca claims the HPET intefer the RTC. Can it be disabled? ( I know some
> > new chipsets implement rtc using HPET).
>
> Basically HPET can operate in legacy mode - where it uses the same IRQ
> as the RTC (and RTC won't deliver any interrupt) - or in "standard"
> mode where the IO-APIC can be configured to deliver the interrupt on
> any line. ATM Linux can only use the legacy mode.
> You can of course disable HPET, but then it won't be available for
> in-kernel timekeeping (in case e.g. the TSC is not stable/synced). I'd
> rather add support for HPET as timer in QEMU...

Something like this. Ulrich can you give it a try:

---
Patch against current GIT, but also applies to kvm-33.
Run kvm with -use-hpet.

qemu/vl.c | 62 ++++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 60 insertions(+), 2 deletions(-)

diff --git a/qemu/vl.c b/qemu/vl.c
index 4ad39f1..36628af 100644
--- a/qemu/vl.c
+++ b/qemu/vl.c
@@ -54,6 +54,7 @@
#include <pty.h>
#include <malloc.h>
#include <linux/rtc.h>
+#include <linux/hpet.h>
#include <linux/ppdev.h>
#endif
#endif
@@ -996,8 +997,9 @@ static void host_alarm_handler(int host_signum)

static int use_rtc = 1;
static int rtc_fd;
+static int use_hpet;

-static int start_rtc_timer(void)
+static int enable_rtc(void)
{
rtc_fd = open("/dev/rtc", O_RDONLY);
if (rtc_fd < 0)
@@ -1017,6 +1019,56 @@ static int start_rtc_timer(void)
return 0;
}

+static char default_hpet[] = "/dev/hpet";
+
+static int enable_hpet(void)
+{
+ struct hpet_info info;
+ int r;
+
+ rtc_fd = open(default_hpet, O_RDONLY);
+ if (rtc_fd < 0)
+ return -1;
+
+ /* Set frequency */
+ r = ioctl(rtc_fd, HPET_IRQFREQ, RTC_FREQ);
+ if (r < 0) {
+ fprintf(stderr, "Could not configure '/dev/hpet' to have a 1024 Hz timer. This is not a fatal\n"
+ "error, but for better emulation accuracy type:\n"
+ "'echo 1024 > /proc/sys/dev/hpet/max-user-freq' as root.\n");
+ goto fail;
+ }
+
+ /* Check capabilities */
+ r = ioctl(rtc_fd, HPET_INFO, &info);
+ if (r < 0)
+ goto fail;
+
+ /* Enable peridic mode */
+ r = ioctl(rtc_fd, HPET_EPI, 0);
+ if (info.hi_flags && (r < 0))
+ goto fail;
+
+ /* Enable interrupt */
+ r = ioctl(rtc_fd, HPET_IE_ON, 0);
+ if (r < 0)
+ goto fail;
+
+ pit_min_timer_count = PIT_FREQ / RTC_FREQ;
+
+ return 0;
+fail:
+ close(rtc_fd);
+ return -1;
+}
+
+static int start_rtc_timer(void)
+{
+ if (use_hpet)
+ return enable_hpet();
+ else
+ return enable_rtc();
+}
#else

static int start_rtc_timer(void)
@@ -1090,7 +1142,7 @@ static void init_timer_alarm(void)
2.6 kernels */
if (itv.it_interval.tv_usec > 1000 || 1) {
/* try to use /dev/rtc to have a faster timer */
- if (!use_rtc || (start_rtc_timer() < 0))
+ if ((!use_rtc && !use_hpet) || (start_rtc_timer() < 0))
goto use_itimer;
/* disable itimer */
itv.it_interval.tv_sec = 0;
@@ -6482,6 +6534,7 @@ void help(void)
"-tdf inject timer interrupts that got lost\n"
#if defined(__linux__)
"-no-rtc don't use /dev/rtc for timer alarm (do use gettimeofday)\n"
+ "-use-rtc use /dev/hpet (HPET) for timer alarm (do use gettimeofday)\n"
#endif
"-option-rom rom load a file, rom, into the option ROM space\n"
"\n"
@@ -6574,6 +6627,7 @@ enum {
QEMU_OPTION_tdf,
#if defined(__linux__)
QEMU_OPTION_no_rtc,
+ QEMU_OPTION_use_hpet,
#endif
QEMU_OPTION_cpu_vendor,
};
@@ -6671,6 +6725,7 @@ const QEMUOption qemu_options[] = {
{ "tdf", 0, QEMU_OPTION_tdf }, /* enable time drift fix */
#if defined(__linux__)
{ "no-rtc", 0, QEMU_OPTION_no_rtc },
+ { "use-hpet", 0, QEMU_OPTION_use_hpet },
#endif
{ "cpu-vendor", HAS_ARG, QEMU_OPTION_cpu_vendor },
{ NULL },
@@ -7395,6 +7450,9 @@ int main(int argc, char **argv)
case QEMU_OPTION_no_rtc:
use_rtc = 0;
break;
+ case QEMU_OPTION_use_hpet:
+ use_hpet = 1;
+ break;
#endif
case QEMU_OPTION_cpu_vendor:
cpu_vendor_string = optarg;

Luca
--
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And I was looking at me
Saw heaven and hell were lies
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