Re: [PATCH 6/9] zbd: consolidate zone mutex initialisation

[Alexey Dobriyan <adobriyan@gmail.com>]

On Mon, May 11, 2020 at 01:16:04AM +0000, Damien Le Moal wrote:
> On 2020/05/06 2:56, Alexey Dobriyan wrote:
> > Initialise everything that is not write pointers coming from device or
> > faked separatedly.
> 
> s/Initialise/Initialize
> s/separatedly/separately

>  	assert(td->o.zone_mode == ZONE_MODE_ZBD);
> > @@ -546,11 +533,25 @@ static int zbd_create_zone_info(struct thread_data *td, struct fio_file *f)
> >  		return -EINVAL;
> >  	}
> >  
> > -	if (ret == 0) {
> > -		f->zbd_info->model = zbd_model;
> > -		f->zbd_info->max_open_zones = td->o.max_open_zones;
> > +	if (ret)
> > +		return ret;
> > +
> > +	zbd = f->zbd_info;
> > +	zbd->model = zbd_model;
> > +	zbd->max_open_zones = td->o.max_open_zones;
> > +
> > +	pthread_mutexattr_init(&attr);
> > +	pthread_mutexattr_setpshared(&attr, true);
> > +	pthread_mutex_init(&zbd->mutex, &attr);
> > +	pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE);
> > +	for (uint32_t z = 0; z < zbd->nr_zones; z++) {
> > +		struct fio_zone_info *zi = &zbd->zone_info[z];
> > +
> > +		pthread_mutex_init(&zi->mutex, &attr);
> >  	}
> > -	return ret;
> > +	pthread_mutexattr_destroy(&attr);
> > +
> > +	return 0;
> >  }
> >  
> >  void zbd_free_zone_info(struct fio_file *f)
> > 
> 
> On a very large drive (e.g. 20TB SMR), we have in excess of 70000 zones. Having
> to loop over all of them again will start to be painful and likely slow down (a
> little) startup. And going forward with ever increasing disk capacity, this will
> get even worse. So not sure if this patch makes much sense.

It separates hw-specific code (reading write pointers) from fio-specific
code.

Iterating can be made faster by going over zone in [->min_zone, ->max_zone)
only, but I didn't look at it.