Re: [PATCH v9 3/9] PCI: Create PCI library functions in support of DOE mailboxes.

[Davidlohr Bueso]

On Tue, 31 May 2022, Davidlohr Bueso wrote:

> On Tue, 31 May 2022, ira.weiny@xxxxxxxxx wrote:
>
> > +static void doe_statemachine_work(struct work_struct *work)
> > +{
> > +	struct delayed_work *w = to_delayed_work(work);
> > +	struct pci_doe_mb *doe_mb = container_of(w, struct pci_doe_mb,
> > +						 statemachine);
> > +	struct pci_dev *pdev = doe_mb->pdev;
> > +	int offset = doe_mb->cap_offset;
> > +	struct pci_doe_task *task;
> > +	u32 val;
> > +	int rc;
> > +
> > +	mutex_lock(&doe_mb->task_lock);
> > +	task = doe_mb->cur_task;
> > +	mutex_unlock(&doe_mb->task_lock);
>
> Instead of a mutex, would it be better to use a rwsem here to protect
> the state machine and allow for concurrent reads for the work callback?
> It is a general interface and a trivial change, but not sure how much
> performance is cared about.

Actually why is this a sleeping lock at all? Afaict all critical regions
are short and just deal with loads and stores of oe_mb->task_lock (and
pci_doe_submit_task also checks the doe_mb->flags with the lock held).
This could be a spinlock or similarly a rwlock.

Thanks,
Davidlohr