Kick io-thread on qemu_chr_accept_input

Once a chr frontend is able to receive input again, we need to inform the io-thread about this fact. Otherwise, main_loop_wait may continue to select without the related backend file descriptor in its set. This can cause high input latencies if only low-rate events arrive otherwise.

Signed-off-by Jan Kiszka<[email protected]>

---

/me wonders if a similar issue explains the slirp slowness under KVM with in-kernel irqchip enabled. Need to check...

  qemu-char.c |    1 +
  1 files changed, 1 insertions(+), 0 deletions(-)

qemu-char.c +1 -0

index 9a5be75..a589a84 100644
@@ -177,6 +177,7 @@ void qemu_chr_accept_input(CharDriverState *s)
  {
      if (s->chr_accept_input)
          s->chr_accept_input(s);
+    qemu_notify_event();
  }
 
  void qemu_chr_fe_printf(CharDriverState *s, const char *fmt, ...)

Quoted 6 lines · Jan Kiszka

Once a chr frontend is able to receive input again, we need to inform the io-thread about this fact. Otherwise, main_loop_wait may continue to select without the related backend file descriptor in its set. This can cause high input latencies if only low-rate events arrive otherwise.

Signed-off-by Jan Kiszka<[email protected]>

I'm not nacking this patch, but please note that this is a band-aid as not all char devices actually use qemu_chr_accept_input().

Quoted 6 lines · Anthony Liguori

Quoted 5 lines · Jan Kiszka

Once a chr frontend is able to receive input again, we need to inform the io-thread about this fact. Otherwise, main_loop_wait may continue to select without the related backend file descriptor in its set. This can cause high input latencies if only low-rate events arrive otherwise.

Quoted 4 lines

Quoted 1 line

Signed-off-by Jan Kiszka<[email protected]>

I'm not nacking this patch, but please note that this is a band-aid as not all char devices actually use qemu_chr_accept_input().

Then they have to be fixed. :)