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Date: Tue, 22 May 2012 19:48:39 +1000
Message-ID: <CAN05THSfrtm1NGQRANiUgj-sihzuOwudu3CPduKAevhf1Cndng@mail.gmail.com>
From: ronnie sahlberg <ronniesahlberg@gmail.com>
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Subject: Re: [Qemu-devel] Weird iscsi/fd-event issue since recent merge of
 event system changes
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Stefan Hajnoczi <stefanha@gmail.com>, qemu-devel <qemu-devel@nongnu.org>, Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>

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, =A0when 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)
>> =A0{
>> =A0 =A0 =A0struct iscsi_context *iscsi =3D iscsilun->iscsi;
>>
>> + =A0 =A0if (iscsi_which_events(iscsi) & POLLOUT) {
>> + =A0 =A0 =A0 =A0iscsi_process_write(iscsilun);
>> + =A0 =A0}
>> +
>> =A0 =A0 =A0qemu_aio_set_fd_handler(iscsi_get_fd(iscsi), iscsi_process_re=
ad,
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 (iscsi_which_eve=
nts(iscsi) & POLLOUT)
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ? iscsi_process_=
write : NULL,
>
> Doh, now I remember. =A0Whenever 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 ne=
eded.


regards
ronnie sahlberg