On Tuesday, January 22, 2019 7:39:21 PM CET Alexander Duyck wrote: > Probe devices asynchronously instead of the driver. This results in us > seeing the same behavior if the device is registered before the driver or > after. This way we can avoid serializing the initialization should the > driver not be loaded until after the devices have already been added. > > The motivation behind this is that if we have a set of devices that > take a significant amount of time to load we can greatly reduce the time to > load by processing them in parallel instead of one at a time. In addition, > each device can exist on a different node so placing a single thread on one > CPU to initialize all of the devices for a given driver can result in poor > performance on a system with multiple nodes. > > This approach can reduce the time needed to scan SCSI LUNs significantly. > The only way to realize that speedup is by enabling more concurrency which > is what is achieved with this patch. > > To achieve this it was necessary to add a new member "async_driver" to the > device_private structure to store the driver pointer while we wait on the > deferred probe call. > > Reviewed-by: Bart Van Assche <[email protected]> > Reviewed-by: Dan Williams <[email protected]> > Signed-off-by: Alexander Duyck <[email protected]>
Reviewed-by: Rafael J. Wysocki <[email protected]> > --- > drivers/base/base.h | 2 ++ > drivers/base/bus.c | 23 +++-------------------- > drivers/base/dd.c | 43 +++++++++++++++++++++++++++++++++++++++++++ > 3 files changed, 48 insertions(+), 20 deletions(-) > > diff --git a/drivers/base/base.h b/drivers/base/base.h > index b6966511b0ca..b405436ee28e 100644 > --- a/drivers/base/base.h > +++ b/drivers/base/base.h > @@ -65,6 +65,7 @@ struct driver_private { > * binding of drivers which were unable to get all the resources needed by > * the device; typically because it depends on another driver getting > * probed first. > + * @async_driver - pointer to device driver awaiting probe via async_probe > * @device - pointer back to the struct device that this structure is > * associated with. > * @dead - This device is currently either in the process of or has been > @@ -80,6 +81,7 @@ struct device_private { > struct klist_node knode_bus; > struct klist_node knode_class; > struct list_head deferred_probe; > + struct device_driver *async_driver; > struct device *device; > u8 dead:1; > }; > diff --git a/drivers/base/bus.c b/drivers/base/bus.c > index cfa5b63b5582..0a58e969f8b7 100644 > --- a/drivers/base/bus.c > +++ b/drivers/base/bus.c > @@ -610,17 +610,6 @@ static ssize_t uevent_store(struct device_driver *drv, > const char *buf, > } > static DRIVER_ATTR_WO(uevent); > > -static void driver_attach_async(void *_drv, async_cookie_t cookie) > -{ > - struct device_driver *drv = _drv; > - int ret; > - > - ret = driver_attach(drv); > - > - pr_debug("bus: '%s': driver %s async attach completed: %d\n", > - drv->bus->name, drv->name, ret); > -} > - > /** > * bus_add_driver - Add a driver to the bus. > * @drv: driver. > @@ -653,15 +642,9 @@ int bus_add_driver(struct device_driver *drv) > > klist_add_tail(&priv->knode_bus, &bus->p->klist_drivers); > if (drv->bus->p->drivers_autoprobe) { > - if (driver_allows_async_probing(drv)) { > - pr_debug("bus: '%s': probing driver %s > asynchronously\n", > - drv->bus->name, drv->name); > - async_schedule(driver_attach_async, drv); > - } else { > - error = driver_attach(drv); > - if (error) > - goto out_unregister; > - } > + error = driver_attach(drv); > + if (error) > + goto out_unregister; > } > module_add_driver(drv->owner, drv); > > diff --git a/drivers/base/dd.c b/drivers/base/dd.c > index 34556359c7da..627ad05064e0 100644 > --- a/drivers/base/dd.c > +++ b/drivers/base/dd.c > @@ -925,6 +925,30 @@ int device_driver_attach(struct device_driver *drv, > struct device *dev) > return ret; > } > > +static void __driver_attach_async_helper(void *_dev, async_cookie_t cookie) > +{ > + struct device *dev = _dev; > + struct device_driver *drv; > + int ret = 0; > + > + __device_driver_lock(dev, dev->parent); > + > + drv = dev->p->async_driver; > + > + /* > + * If device has been removed or someone has already successfully > + * bound a driver before us just skip the driver probe call. > + */ > + if (!dev->p->dead && !dev->driver) > + ret = driver_probe_device(drv, dev); > + > + __device_driver_unlock(dev, dev->parent); > + > + dev_dbg(dev, "driver %s async attach completed: %d\n", drv->name, ret); > + > + put_device(dev); > +} > + > static int __driver_attach(struct device *dev, void *data) > { > struct device_driver *drv = data; > @@ -952,6 +976,25 @@ static int __driver_attach(struct device *dev, void > *data) > return ret; > } /* ret > 0 means positive match */ > > + if (driver_allows_async_probing(drv)) { > + /* > + * Instead of probing the device synchronously we will > + * probe it asynchronously to allow for more parallelism. > + * > + * We only take the device lock here in order to guarantee > + * that the dev->driver and async_driver fields are protected > + */ > + dev_dbg(dev, "probing driver %s asynchronously\n", drv->name); > + device_lock(dev); > + if (!dev->driver) { > + get_device(dev); > + dev->p->async_driver = drv; > + async_schedule(__driver_attach_async_helper, dev); > + } > + device_unlock(dev); > + return 0; > + } > + > device_driver_attach(drv, dev); > > return 0; > >
