[patch 1/2] QEMU: use SIGARLM for alarm timers, enable SIGIO on qemu_set_fd_handler2()

Marcelo Tosatti
2008-04-11T18:38:53Z

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From: Anders Melchiorsen <mail@flac.kalibalik.dk>

Without I/O signals, qemu is relying on periodic timer events to poll
the I/O. That seems wrong, even though it works reasonably well
because timers are so frequent. In KVM, timers are less frequent, and
it does not work quite as well.

Here is a quick try at a more elaborate patch.

It attaches a signal to all[1] file descriptors that will be used in
select(). Also, it uses a dedicated SIGIO handler rather than
piggybacking on the alarm handler, so alarm I/O is changed to use
SIGALRM.

I copied the handler function from the alarm case, quite frankly I do
not quite understand what is going on. Also, I left _WIN32 out, since
I have no idea how signals work there.

[1] The slirp file descriptors are not included yet.

Index: kvm-userspace.io/qemu/vl.c
===================================================================
--- kvm-userspace.io.orig/qemu/vl.c
+++ kvm-userspace.io/qemu/vl.c
@@ -1177,6 +1177,25 @@ static int timer_load(QEMUFile *f, void
return 0;
}

+#ifndef _WIN32
+static void host_io_handler(int host_signum)
+{
+ CPUState *env = next_cpu;
+
+ if (env) {
+ /* stop the currently executing cpu because io occured */
+ cpu_interrupt(env, CPU_INTERRUPT_EXIT);
+#ifdef USE_KQEMU
+ if (env->kqemu_enabled) {
+ kqemu_cpu_interrupt(env);
+ }
+#endif
+ }
+
+ event_pending = 1;
+}
+#endif
+
#ifdef _WIN32
void CALLBACK host_alarm_handler(UINT uTimerID, UINT uMsg,
DWORD_PTR dwUser, DWORD_PTR dw1, DWORD_PTR dw2)
@@ -1270,7 +1289,20 @@ static uint64_t qemu_next_deadline(void)

#define RTC_FREQ 1024

-static void enable_sigio_timer(int fd)
+static void enable_sigio(int fd)
+{
+ struct sigaction act;
+
+ sigfillset(&act.sa_mask);
+ act.sa_flags = 0;
+ act.sa_handler = host_io_handler;
+
+ sigaction(SIGIO, &act, NULL);
+ fcntl(fd, F_SETFL, O_ASYNC);
+ fcntl(fd, F_SETOWN, getpid());
+}
+
+static void enable_sigalrm(int fd)
{
struct sigaction act;

@@ -1279,8 +1311,9 @@ static void enable_sigio_timer(int fd)
act.sa_flags = 0;
act.sa_handler = host_alarm_handler;

- sigaction(SIGIO, &act, NULL);
+ sigaction(SIGALRM, &act, NULL);
fcntl(fd, F_SETFL, O_ASYNC);
+ fcntl(fd, F_SETSIG, SIGALRM);
fcntl(fd, F_SETOWN, getpid());
}

@@ -1317,7 +1350,7 @@ static int hpet_start_timer(struct qemu_
if (r < 0)
goto fail;

- enable_sigio_timer(fd);
+ enable_sigalrm(fd);
t->priv = (void *)(long)fd;

return 0;
@@ -1355,7 +1388,7 @@ static int rtc_start_timer(struct qemu_a
return -1;
}

- enable_sigio_timer(rtc_fd);
+ enable_sigalrm(rtc_fd);

t->priv = (void *)(long)rtc_fd;

@@ -4029,7 +4062,6 @@ static TAPState *net_tap_fd_init(VLANSta
return NULL;
s->fd = fd;
s->no_poll = 0;
- enable_sigio_timer(fd);
s->vc = qemu_new_vlan_client(vlan, tap_receive, NULL, s);
qemu_set_fd_handler2(s->fd, tap_read_poll, tap_send, NULL, s);
snprintf(s->vc->info_str, sizeof(s->vc->info_str), "tap: fd=%d", fd);
@@ -5661,6 +5693,10 @@ int qemu_set_fd_handler2(int fd,
return -1;
ioh->next = first_io_handler;
first_io_handler = ioh;
+#ifndef _WIN32
+ enable_sigio(fd);
+#endif
+
found:
ioh->fd = fd;
ioh->fd_read_poll = fd_read_poll;

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