This code was a pleasure to read, super clean.
On Wed, May 02, 2018 at 11:59:31PM -0400, Pavel Tatashin wrote:
> When system is rebooted, halted or kexeced device_shutdown() is
> called.
>
> This function shuts down every single device by calling either:
> dev->bus->shutdown(dev)
> dev->driver->shutdown(dev)
>
> Even on a machine just with a moderate amount of devices, device_shutdown()
> may take multiple seconds to complete. Because many devices require a
> specific delays to perform this operation.
>
> Here is sample analysis of time it takes to call device_shutdown() on
> two socket Intel(R) Xeon(R) CPU E5-2630 v4 @ 2.20GHz machine.
>
> device_shutdown 2.95s
> mlx4_shutdown1.14s
> megasas_shutdown 0.24s
> ixgbe_shutdown 0.37s x 4 (four ixgbe devices on my machine).
> the rest 0.09s
>
> In mlx4 we spent the most time, but that is because there is a 1 second
> sleep:
> mlx4_shutdown
> mlx4_unload_one
> mlx4_free_ownership
>msleep(1000)
>
> With megasas we spend quoter of second, but sometimes longer (up-to 0.5s)
> in this path:
>
> megasas_shutdown
> megasas_flush_cache
> megasas_issue_blocked_cmd
> wait_event_timeout
>
> Finally, with ixgbe_shutdown() it takes 0.37 for each device, but that time
> is spread all over the place, with bigger offenders:
>
> ixgbe_shutdown
> __ixgbe_shutdown
> ixgbe_close_suspend
> ixgbe_down
> ixgbe_init_hw_generic
> ixgbe_reset_hw_X540
> msleep(100);0.104483472
> ixgbe_get_san_mac_addr_generic 0.048414851
> ixgbe_get_wwn_prefix_generic0.048409893
> ixgbe_start_hw_X540
> ixgbe_start_hw_generic
> ixgbe_clear_hw_cntrs_generic 0.048581502
> ixgbe_setup_fc_generic0.024225800
>
> All the ixgbe_*generic functions end-up calling:
> ixgbe_read_eerd_X540()
> ixgbe_acquire_swfw_sync_X540
> usleep_range(5000, 6000);
> ixgbe_release_swfw_sync_X540
> usleep_range(5000, 6000);
>
> While these are short sleeps, they end-up calling them over 24 times!
> 24 * 0.0055s = 0.132s. Adding-up to 0.528s for four devices.
>
> While we should keep optimizing the individual device drivers, in some
> cases this is simply a hardware property that forces a specific delay, and
> we must wait.
>
> So, the solution for this problem is to shutdown devices in parallel.
> However, we must shutdown children before shutting down parents, so parent
> device must wait for its children to finish.
>
> With this patch, on the same machine devices_shutdown() takes 1.142s, and
> without mlx4 one second delay only 0.38s
>
> Signed-off-by: Pavel Tatashin
> ---
> drivers/base/core.c | 238 +++-
> 1 file changed, 189 insertions(+), 49 deletions(-)
>
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index b610816eb887..f370369a303b 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -25,6 +25,7 @@
> #include
> #include
> #include
> +#include
>
> #include "base.h"
> #include "power/power.h"
> @@ -2102,6 +2103,59 @@ const char *device_get_devnode(struct device *dev,
> return *tmp = s;
> }
>
> +/**
> + * device_children_count - device children count
> + * @parent: parent struct device.
> + *
> + * Returns number of children for this device or 0 if nonde.
> + */
> +static int device_children_count(struct device *parent)
> +{
> + struct klist_iter i;
> + int children = 0;
> +
> + if (!parent->p)
> + return 0;
> +
> + klist_iter_init(&parent->p->klist_children, &i);
> + while (next_device(&i))
> + children++;
> + klist_iter_exit(&i);
> +
> + return children;
> +}
> +
> +/**
> + * device_get_child_by_index - Return child using the provide index.
> + * @parent: parent struct device.
> + * @index: Index of the child, where 0 is the first child in the children
> list,
> + * and so on.
> + *
> + * Returns child or NULL if child with this index is not present.
> + */
> +static struct device *
> +device_get_child_by_index(struct device *parent, int index)
> +{
> + struct klist_iter i;
> + struct device *dev = NULL, *d;
> + int child_index = 0;
> +
> + if (!parent->p || index < 0)
> + return NULL;
> +
> + klist_iter_init(&parent->p->klist_children, &i);
> + while ((d = next_device(&i)) != NULL) {
perhaps:
while ((d = next_device(&i))) {
> + if (child_index == index) {
> + dev = d;
> + break;
> + }
> + child_index++;
> + }
> + klist_iter_exit(&i);
> +
> + return dev;
> +}
> +
> /**
> * device_for_each_child - device child iterator.
> * @parent: parent struct device.
> @@ -2765,71 +281
