Re: [dpdk-stable] [PATCH] vdpa/mlx5: fix configuration mutex cleanup

[Matan Azrad <matan@nvidia.com>]

From: Maxime Coquelin
> On 1/14/21 4:23 PM, Matan Azrad wrote:
> >
> >
> > From: Maxime Coquelin
> >> On 1/14/21 2:09 PM, Matan Azrad wrote:
> >>>
> >>>
> >>> From: Maxime Coquelin
> >>>> Hi Matan,
> >>>>
> >>>> On 1/14/21 12:49 PM, Matan Azrad wrote:
> >>>>> Hi Maxime and David
> >>>>>
> >>>>> Thank you for Review.
> >>>>>
> >>>>> From: David Marchand
> >>>>>> On Fri, Jan 8, 2021 at 9:48 AM David Marchand
> >>>>>> <david.marchand@redhat.com> wrote:
> >>>>>>>> I wonder if it would be possible and cleaner to disable
> >>>>>>>> cancellation on the thread while the mutex is held?
> >>>>>
> >>>>> Yes, we can cause thread to return by some global variable sync.
> >>>>> It is the same logic.
> >>>>
> >>>> No, that was not my suggestion. My suggestion is to block the
> >>>> thread cancellation while in the critical section, using
> pthread_setcancelstate().
> >>>
> >>> Yes, Generally it is better to let the thread control his
> >>> cancellation, either
> >> cancel itself or enabling\disabling cancellations.
> >>>
> >>> I don't see a reason to wait for the thread in current logic - the
> >>> critical section
> >> is not important to be completed here.
> >>
> >> The reason I see is there are quite a few things done in this
> >> critical section. And if tomorrow someone add new things in it, he
> >> may not know the thread can be cancelled at any time, which could cause
> hard to debug issues.
> >
> > As I said, here it is not needed, this thread designed just to cause guest
> notifications.
> >
> > The optional future developer mistake can be done also outside the critical
> section in in any other place - we cannot protect it.
> >
> > The design choice is to close the thread fast.
> 
> But why is it so urgent that it cannot been stopped cleanly?
> I don't think it would add seconds delay by doing it in a clean way.

We have system calls there per queue.
No need this optional delay just because of mutex cleaning. 


 
> Thanks,
> Maxime
> 
> >>> We just want to close the thread and to clean the mutex.
> >>>
> >>>>>>> +1
> >>>>>>
> >>>>>> IEEE Std 1003.1-2001/Cor 2-2004, item XBD/TC2/D6/26 is applied,
> >>>>>> adding pthread_t to the list of types that are not required to be
> >>>>>> arithmetic types, thus allowing pthread_t to be defined as a structure.
> >>>>>>
> >>>>>> It would be better to leave pthread_t alone and not interpret it:
> >>>>>>
> >>>>>> if (priv->timer_tid) {
> >>>>>>     pthread_cancel(priv->timer_tid);
> >>>>>>     pthread_join(priv->timer_tid, &status); }
> >>>>>> priv->timer_tid = 0;
> >>>>>
> >>>>>
> >>>>> I'm not sure why you think it is better in this specific case.
> >>>>> The cancellation will close the thread in faster way, no need to
> >>>>> wait for the
> >>>> thread to close itself.
> >>>>>
> >>>>>
> >>>>>>
> >>>>>> --
> >>>>>> David Marchand
> >>>>>
> >>>
> >