Re: [Qemu-devel] Weird iscsi/fd-event issue since recent merge of event system changes

[ronnie sahlberg <ronniesahlberg@gmail.com>]

None of the other drivers in block/*.c call qemu_notify_event()

Do you you think those should be audited and have this call added to
where required ?


regards
ronnie sahlberg

On Tue, May 22, 2012 at 7:48 PM, ronnie sahlberg
<ronniesahlberg@gmail.com> wrote:
> On Tue, May 22, 2012 at 7:29 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>> Il 22/05/2012 11:15, ronnie sahlberg ha scritto:
>>> Hi,
>>>
>>> Now that I see what happens, I can easily workaround this in block/iscsi.c
>>> by the patch below, but I dont know if this is the right thing to do.
>>>
>>> It does appear that here,  when I use qemu_set_fd_handler() and add a
>>> handler for "writeble" it takes 55ms before the event system notices
>>> this and reacts.
>>>
>>>
>>>
>>> diff --git a/block/iscsi.c b/block/iscsi.c
>>> index d37c4ee..1ebff0f 100644
>>> --- a/block/iscsi.c
>>> +++ b/block/iscsi.c
>>> @@ -105,6 +105,10 @@ iscsi_set_events(IscsiLun *iscsilun)
>>>  {
>>>      struct iscsi_context *iscsi = iscsilun->iscsi;
>>>
>>> +    if (iscsi_which_events(iscsi) & POLLOUT) {
>>> +        iscsi_process_write(iscsilun);
>>> +    }
>>> +
>>>      qemu_aio_set_fd_handler(iscsi_get_fd(iscsi), iscsi_process_read,
>>>                             (iscsi_which_events(iscsi) & POLLOUT)
>>>                             ? iscsi_process_write : NULL,
>>
>> Doh, now I remember.  Whenever you change the aio handlers you need to
>> call qemu_notify_event() afterwards, if the handler may fire right away.
>
> Thanks.  I just confirmed that qemu_notify_event() fixes the issue.
> Ill send a patch that uses qemu_notify_event() and a comment why this is needed.
>
>
> regards
> ronnie sahlberg