linux-kernel - Re: [PATCH 1/2] ixgbe: release lock for the duration of ixgbe_suspend

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Date:   Thu, 3 May 2018 06:20:07 -0700
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     Pavel Tatashin <pasha.tatashin@...cle.com>
Cc:     steven.sistare@...cle.com, daniel.m.jordan@...cle.com,
        LKML <linux-kernel@...r.kernel.org>,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
        intel-wired-lan <intel-wired-lan@...ts.osuosl.org>,
        Netdev <netdev@...r.kernel.org>,
        Greg KH <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 1/2] ixgbe: release lock for the duration of ixgbe_suspend_close()

On Wed, May 2, 2018 at 8:59 PM, Pavel Tatashin
<pasha.tatashin@...cle.com> wrote:
> Currently, during device_shutdown() ixgbe holds rtnl_lock for the duration
> of lengthy ixgbe_close_suspend(). On machines with multiple ixgbe cards
> this lock prevents scaling if device_shutdown() function is multi-threaded.
>
> It is not necessary to hold this lock during ixgbe_close_suspend()
> as it is not held when ixgbe_close() is called also during shutdown but for
> kexec case.
>
> Signed-off-by: Pavel Tatashin <pasha.tatashin@...cle.com>
> ---
>  drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> index afadba99f7b8..e7875b58854b 100644
> --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> @@ -6748,8 +6748,15 @@ static int __ixgbe_shutdown(struct pci_dev *pdev, bool *enable_wake)
>         rtnl_lock();
>         netif_device_detach(netdev);
>
> -       if (netif_running(netdev))
> +       if (netif_running(netdev)) {
> +               /* Suspend takes a long time, device_shutdown may be
> +                * parallelized this function, so drop lock for the
> +                * duration of this call.
> +                */
> +               rtnl_unlock();
>                 ixgbe_close_suspend(adapter);
> +               rtnl_lock();
> +       }
>
>         ixgbe_clear_interrupt_scheme(adapter);
>         rtnl_unlock();

I'm not a fan of dropping the mutex while we go through
ixgbe_close_suspend. I'm concerned it will result in us having a
number of races on shutdown.

If anything, I think we would need to find a replacement for the mutex
that can operate at the per-netdev level if you are wanting to
parallelize this.

- Alex