Am 04.05.2010 um 16:34 schrieb Anthony Liguori <anth...@codemonkey.ws>:
On 05/04/2010 09:30 AM, Alexander Graf wrote:
Am 04.05.2010 um 15:44 schrieb Anthony Liguori
<anth...@codemonkey.ws>:
On 04/20/2010 11:56 AM, Alexander Graf wrote:
Virtio-Console can only process one character at a time. Using it
on S390
gave me strage "lags" where I got the character I pressed before
when
pressing one. So I typed in "abc" and only received "a", then
pressed "d"
but the guest received "b" and so on.
While the stdio driver calls a poll function that just processes
on its
queue in case virtio-console can't take multiple characters at
once, the
muxer does not have such callbacks, so it can't empty its queue.
To work around that limitation, I introduced a new timer that
only gets
active when the guest can not receive any more characters. In
that case
it polls again after a while to check if the guest is now
receiving input.
This patch fixes input when using -nographic on s390 for me.
I think this is really a kvm issue. I assume it's because s390
idles in the kernel so you never drop to userspace to repoll the
descriptor.
There is no polling for the muxer. That's why it never knows when
virtio-console can receive again.
Maybe I'm missing something simple, but it looks to me like the
muxer is polling. mux_chr_can_read() is going to eventually poll
the muxed devices to figure this out.
If the root of the problem is that mux_chr_can_read() isn't being
invoked for a prolonged period of time, the real issue is the
problem I described.
The problem is that the select list of fds includes the stdio fd, so
that gets notified and is coupled with virtio-console, but there's
nothing passing that on to mux and I don't think it'd be clever to
expose internal data to the muxer to tell it about the backend fds.
Alex
Regards,
Anthony Liguori
This patch basically adfs timer based polling for that exact case.
Alex
A timer is a hacky solution. You really need to use an io thread
to solve this and then you need to switch away from
qemu_set_fd_handler2 to qemu_set_fd_handler() and make sure that
the later breaks select whenever it's invoked.
Regards,
Anthony Liguori
---
Please consider for stable.
---
qemu-char.c | 10 ++++++++++
1 files changed, 10 insertions(+), 0 deletions(-)
diff --git a/qemu-char.c b/qemu-char.c
index 05df971..ce9df3a 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -235,6 +235,7 @@ typedef struct {
IOEventHandler *chr_event[MAX_MUX];
void *ext_opaque[MAX_MUX];
CharDriverState *drv;
+ QEMUTimer *accept_timer;
int focus;
int mux_cnt;
int term_got_escape;
@@ -396,6 +397,13 @@ static void mux_chr_accept_input
(CharDriverState *chr)
d->chr_read[m](d->ext_opaque[m],
&d->buffer[m][d->cons[m]++& MUX_BUFFER_MASK], 1);
}
+
+ /* We're still not able to sync producer and consumer, so
let's wait a bit
+ and try again by then. */
+ if (d->prod[m] != d->cons[m]) {
+ qemu_mod_timer(d->accept_timer, qemu_get_clock(vm_clock)
+ + (int64_t)100000);
+ }
}
static int mux_chr_can_read(void *opaque)
@@ -478,6 +486,8 @@ static CharDriverState *qemu_chr_open_mux
(CharDriverState *drv)
chr->opaque = d;
d->drv = drv;
d->focus = -1;
+ d->accept_timer = qemu_new_timer(vm_clock,
+ (QEMUTimerCB*)
mux_chr_accept_input, chr);
chr->chr_write = mux_chr_write;
chr->chr_update_read_handler = mux_chr_update_read_handler;
chr->chr_accept_input = mux_chr_accept_input;
