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

From: Maxime Coquelin

On 1/14/21 4:23 PM, Matan Azrad wrote:

quoted

From: Maxime Coquelin

quoted

On 1/14/21 2:09 PM, Matan Azrad wrote:

quoted

From: Maxime Coquelin

quoted

Hi Matan,

On 1/14/21 12:49 PM, Matan Azrad wrote:

quoted

Hi Maxime and David

Thank you for Review.

From: David Marchand

quoted

On Fri, Jan 8, 2021 at 9:48 AM David Marchand
[off-list ref] wrote:

quoted

quoted

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().

quoted

quoted

quoted

Yes, Generally it is better to let the thread control his
cancellation, either

cancel itself or enabling\disabling cancellations.

quoted

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.

quoted

As I said, here it is not needed, this thread designed just to cause guest

notifications.

quoted

The optional future developer mistake can be done also outside the critical

section in in any other place - we cannot protect it.

quoted

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

quoted

quoted

quoted

We just want to close the thread and to clean the mutex.

quoted

quoted

quoted

quoted

+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.

quoted

quoted

--
David Marchand