[Qemu-devel] [PATCH] Add support for HPET periodic timer.

[Qemu-devel] [PATCH] Add support for HPET periodic timer.

[Luca Tettamanti]

Linux operates the HPET timer in legacy replacement mode, which means that the
periodic interrupt of the CMOS RTC is not delivered (qemu won't be able to use
/dev/rtc). Add support for HPET (/dev/hpet) as a replacement for the RTC; the
periodic interrupt is delivered via SIGIO and is handled in the same way as the
RTC timer.
HPET must be explicitly enabled with -use-hpet.

Signed-off-by: Luca Tettamanti <kronos.it@gmail.com>
---
 qemu/vl.c |   62 +++++++++++++++++++++++++++++++++++++++++++++++++-
 1 files changed, 60 insertions(+), 2 deletions(-)

diff --git a/qemu/vl.c b/qemu/vl.c
index 4ad39f1..db7262b 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 periodic 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-hpet       use /dev/hpet (HPET) instead of RTC for timer alarm\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;
-- 
1.5.2.3

[Qemu-devel] Re: [kvm-devel] [PATCH] Add support for HPET periodic timer.

[Avi Kivity]

Luca Tettamanti wrote:
> Linux operates the HPET timer in legacy replacement mode, which means that the
> periodic interrupt of the CMOS RTC is not delivered (qemu won't be able to use
> /dev/rtc). Add support for HPET (/dev/hpet) as a replacement for the RTC; the
> periodic interrupt is delivered via SIGIO and is handled in the same way as the
> RTC timer.
> HPET must be explicitly enabled with -use-hpet.
>
>   

Are there any downsides to using HPET?  If not, I suggest making it the 
default, in order to reduce complexity for the user.

Something like:

- try to use HPET (unless -no-rtc selected)
- try to use RTC  (unless -no-rtc selected)
- fallback to normal unix facilities

-- 
error compiling committee.c: too many arguments to function

[Qemu-devel] Re: [kvm-devel] [PATCH] Add support for HPET periodic timer.

[Daniel P. Berrange]

On Mon, Aug 13, 2007 at 11:04:46AM +0300, Avi Kivity wrote:
> Luca Tettamanti wrote:
> > Linux operates the HPET timer in legacy replacement mode, which means that the
> > periodic interrupt of the CMOS RTC is not delivered (qemu won't be able to use
> > /dev/rtc). Add support for HPET (/dev/hpet) as a replacement for the RTC; the
> > periodic interrupt is delivered via SIGIO and is handled in the same way as the
> > RTC timer.
> > HPET must be explicitly enabled with -use-hpet.
> >
> >   
> 
> Are there any downsides to using HPET?  If not, I suggest making it the 
> default, in order to reduce complexity for the user.

Only downside is that not all machines have HPET, and many which do have it
disabled in BIOS for 'compatability' with Windows, but if you always fallback
to trying RTC too, that's not an issue.

> Something like:
> 
> - try to use HPET (unless -no-rtc selected)
> - try to use RTC  (unless -no-rtc selected)
> - fallback to normal unix facilities

If we're going to add command line args it probably makes sense  to be a
little more generic than -no-rtc or -use-hpet. Have a list of preferred
clock sources eg

  -clock hpet,rtc,unix

If -clock is omitted, then default to trying all in the priority you
describe.

Dan.
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[Qemu-devel] Re: [kvm-devel] [PATCH] Add support for HPET periodic timer.

[Luca]

On 8/13/07, Daniel P. Berrange <berrange@redhat.com> wrote:
> On Mon, Aug 13, 2007 at 11:04:46AM +0300, Avi Kivity wrote:
> > Luca Tettamanti wrote:
> > Something like:
> >
> > - try to use HPET (unless -no-rtc selected)
> > - try to use RTC  (unless -no-rtc selected)
> > - fallback to normal unix facilities
>
> If we're going to add command line args it probably makes sense  to be a
> little more generic than -no-rtc or -use-hpet. Have a list of preferred
> clock sources eg
>
>   -clock hpet,rtc,unix
>
> If -clock is omitted, then default to trying all in the priority you
> describe.

Makes sense, I'll prepare a patch (maybe after a couple of days of vacation :P).

Luca