lkml.org 
[lkml]   [2018]   [May]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v4 1/1] drivers core: multi-threading device shutdown
On Mon, May 14, 2018 at 03:42:54PM -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 with just a moderate amount of devices, device_shutdown()
> may take multiple seconds to complete. This is because many devices require
> a specific delays to perform this operation.
>
> Here is a sample analysis of time it takes to call device_shutdown() on a
> two socket Intel(R) Xeon(R) CPU E5-2630 v4 @ 2.20GHz machine.
>
> device_shutdown 2.95s
> -----------------------------
> mlx4_shutdown 1.14s
> megasas_shutdown 0.24s
> ixgbe_shutdown 0.37s x 4 (four ixgbe devices on this machine).
> the rest 0.09s
>
> In mlx4 we spent the most time, but that is because there is a 1 second
> sleep, which is defined by hardware specifications:
> mlx4_shutdown
> mlx4_unload_one
> mlx4_free_ownership
> msleep(1000)
>
> With megasas we spend a quarter of a 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_generic 0.048409893
> ixgbe_start_hw_X540
> ixgbe_start_hw_generic
> ixgbe_clear_hw_cntrs_generic 0.048581502
> ixgbe_setup_fc_generic 0.024225800
>
> 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. Also we have
> four msleep(100). Totaling to: 0.928s
>
> 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
>
> This feature can be optionally disabled via kernel parameter:
> device_shutdown_serial. When booted with this parameter, device_shutdown()
> will shutdown devices one by one.
>
> Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com>
> ---
> drivers/base/core.c | 292 ++++++++++++++++++++++++++++++++++++--------
> 1 file changed, 242 insertions(+), 50 deletions(-)

Can you refactor this to be at least 2 patches? One that moves code
around to comon functions to make the second patch, that adds the new
functionality, easier to review and understand?

And I echo the "don't use kerneldoc for static functions" review
comment, that's not needed at all.

thanks,

greg k-h

\
 
 \ /
  Last update: 2018-05-15 09:38    [W:0.079 / U:0.508 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site