[dpdk-dev] [PATCH 0/2] provide thread unsafe async registration functions

[Maxime Coquelin]

Hi Jiayu,

On 6/7/21 10:07 AM, Hu, Jiayu wrote:
> Hi Maxime,
> 
>> -----Original Message-----
>> From: Maxime Coquelin <mcoqueli at redhat.com>
>> Sent: Friday, June 4, 2021 3:25 PM
>> To: Hu, Jiayu <jiayu.hu at intel.com>; dev at dpdk.org
>> Cc: maxime.coquelin at redhat.com; Xia, Chenbo <chenbo.xia at intel.com>;
>> Wang, Yinan <yinan.wang at intel.com>
>> Subject: Re: [PATCH 0/2] provide thread unsafe async registration functions
>>
>> Sorry, for previous blank reply.
>>
>> On 5/28/21 10:11 AM, Jiayu Hu wrote:
>>> Lock protection is needed during the vhost notifies the application of
>>> device readiness, so the first patch is to add lock protection. After
>>> performing locking, existed async vhost registration functions will cause
>>> deadlock, as they acquire lock too. So the second patch is to provide
>>> unsafe registration functions to support calling within vhost callback
>>> functions.
>>
>> I agree the callback should be always protected, and in that case having
>> a new thread-unsafe API makes sense for async registration.
>>
>> Regarding backport, I'm not sure what we should do.
>>
>> Backporting new API is a no-go, but with only backporting patch 1 async
>> feature will be always broken on 20.11 LTS, right?
> 
> Yes, if only backporting this fix patch to 20.11 LTS, it may break apps who call
> async registration functions inside vhost callbacks.
> 
> How about making this patch not a fix, but a new feature?

Async will be still broken in v20.11 in this case.
Maybe the better thing would be to remove async support in v20.11, as
its support was quite limited in that release anyway. Does that make
sense?

Thanks,
Maxime

> Thanks,
> Jiayu
>>
>> What do you think?
>>
>> Thanks,
>> Maxime
>>
>>> Jiayu Hu (2):
>>>   vhost: fix lock on device readiness notification
>>>   vhost: add thread unsafe async registration functions
>>>
>>>  doc/guides/prog_guide/vhost_lib.rst |  12 +++
>>>  lib/vhost/rte_vhost_async.h         |  42 ++++++++++
>>>  lib/vhost/version.map               |   4 +
>>>  lib/vhost/vhost.c                   | 161 +++++++++++++++++++++++++++---------
>>>  lib/vhost/vhost_user.c              |   5 +-
>>>  5 files changed, 180 insertions(+), 44 deletions(-)
>>>
>