On 05/08/2011 02:22 PM, Ingo Molnar wrote:
>
> * Asias He <asias.hejun@xxxxxxxxx> wrote:
>
>> As virtio spec says:
>>
>> """
>> Because this is high importance and low bandwidth, the current Linux
>> implementation polls for the buffer to be used, rather than waiting
>> for an interrupt, simplifying the implementation signicantly.
>> """
>>
>> drivers/char/virtio_console.c
>> send_buf() {
>> ...
>> /* Tell Host to go! */
>> virtqueue_kick(out_vq);
>> ...
>> while (!virtqueue_get_buf(out_vq, &len))
>> cpu_relax();
>> ...
>> }
>>
>> The console hangs can simply be reproduced by yes command which
>> gives tremendous console IOs and IRQs.
>>
>> [ 16.786440] irq 4: nobody cared (try booting with the "irqpoll" option)
>> [ 16.786440] Pid: 1437, comm: yes Tainted: G W 2.6.39-rc6+ #56
>> [ 16.786440] Call Trace:
>> [ 16.786440] [<c16578eb>] __report_bad_irq+0x30/0x89
>> [ 16.786440] [<c10980e6>] note_interrupt+0x118/0x17a
>> [ 16.786440] [<c1096e7d>] handle_irq_event_percpu+0x168/0x179
>> [ 16.786440] [<c1096eba>] handle_irq_event+0x2c/0x46
>> [ 16.786440] [<c1098516>] ? unmask_irq+0x1e/0x1e
>> [ 16.786440] [<c1098566>] handle_level_irq+0x50/0x6e
>> [ 16.786440] <IRQ> [<c102fa69>] ? do_IRQ+0x35/0x7f
>> [ 16.786440] [<c1665ea9>] ? common_interrupt+0x29/0x30
>> [ 16.786440] [<c16610d6>] ? _raw_spin_unlock_irqrestore+0x7/0x28
>> [ 16.786440] [<c1364f65>] ? hvc_write+0x88/0x9e
>> [ 16.786440] [<c1355500>] ? do_output_char+0x88/0x18a
>> [ 16.786440] [<c1355631>] ? process_output+0x2f/0x42
>> [ 16.786440] [<c1355af6>] ? n_tty_write+0x211/0x2dc
>> [ 16.786440] [<c1059d77>] ? try_to_wake_up+0x226/0x226
>> [ 16.786440] [<c13534a4>] ? tty_write+0x15e/0x1d1
>> [ 16.786440] [<c12c1644>] ? security_file_permission+0x22/0x26
>> [ 16.786440] [<c13558e5>] ? process_echoes+0x241/0x241
>> [ 16.786440] [<c10dd9d2>] ? vfs_write+0x84/0xd7
>> [ 16.786440] [<c1353346>] ? tty_write_lock+0x3d/0x3d
>> [ 16.786440] [<c10ddb92>] ? sys_write+0x3b/0x5d
>> [ 16.786440] [<c166594c>] ? sysenter_do_call+0x12/0x22
>> [ 16.786440] handlers:
>> [ 16.786440] [<c1351397>] (vp_interrupt+0x0/0x3a)
>> [ 16.786440] Disabling IRQ #4
>
> Hm, why is irq #4 active if the guest-side virtio console driver does not
> handle it?
>
>> Signed-off-by: Asias He <asias.hejun@xxxxxxxxx>
>> ---
>> tools/kvm/virtio/console.c | 2 --
>> 1 files changed, 0 insertions(+), 2 deletions(-)
>>
>> diff --git a/tools/kvm/virtio/console.c b/tools/kvm/virtio/console.c
>> index f5449ba..1fecf37 100644
>> --- a/tools/kvm/virtio/console.c
>> +++ b/tools/kvm/virtio/console.c
>> @@ -171,8 +171,6 @@ static void virtio_console_handle_callback(struct kvm *self, void *param)
>> len = term_putc_iov(CONSOLE_VIRTIO, iov, out);
>> virt_queue__set_used_elem(vq, head, len);
>> }
>> -
>> - virt_queue__trigger_irq(vq, virtio_console_pci_device.irq_line, &cdev.isr, self);
>> }
>
> I think this at least requires a comment at that place, that we intentionally
> skip notifying the guest, because Linux guests do not use the console IRQ.
Will do.
> Does the guest-side virtio driver *ever* use the irq?
Yes. They use IRQ at least for the RX path.
> Thanks,
>
> Ingo
>
--
Best Regards,
Asias He
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