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Re: [Qemu-devel] [PATCH] qemu: generate signals on tap I/O
From: |
Anders Melchiorsen |
Subject: |
Re: [Qemu-devel] [PATCH] qemu: generate signals on tap I/O |
Date: |
Sat, 16 Feb 2008 11:58:15 +0100 |
User-agent: |
Gnus/5.1008 (Gnus v5.10.8) XEmacs/21.4.20 (linux) |
Aurelien Jarno <address@hidden> writes:
> The patch below from KVM improves network transfers in a huge way.
> wget in a MIPS target now gives me a transfer speed of up to 120
> Mbits/s with an e1000 emulated card.
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.
Anders.
diff --git a/vl.c b/vl.c
index c87e8bc..ff8ceef 100644
--- a/vl.c
+++ b/vl.c
@@ -1148,6 +1148,25 @@ static int timer_load(QEMUFile *f, void *opaque, int
version_id)
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)
@@ -1240,7 +1259,20 @@ 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;
@@ -1249,8 +1281,9 @@ 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());
}
@@ -1287,7 +1320,7 @@ static int hpet_start_timer(struct qemu_alarm_timer *t)
if (r < 0)
goto fail;
- enable_sigio_timer(fd);
+ enable_sigalrm(fd);
t->priv = (void *)(long)fd;
return 0;
@@ -1325,7 +1358,7 @@ static int rtc_start_timer(struct qemu_alarm_timer *t)
return -1;
}
- enable_sigio_timer(rtc_fd);
+ enable_sigalrm(rtc_fd);
t->priv = (void *)(long)rtc_fd;
@@ -5481,6 +5514,10 @@ 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;