From: Intel-wired-lan <intel-wired-lan-boun...@osuosl.org> on behalf of Przemek
Kitszel <przemyslaw.kits...@intel.com>
Sent: Monday, September 23, 2024 11:07 AM
To: Wander Lairson Costa <wan...@redhat.com>
Cc: Yuying Ma <y...@redhat.com>; moderated list:INTEL ETHERNET DRIVERS
<intel-wired-...@lists.osuosl.org>; open list <linux-ker...@vger.kernel.org>;
Eric Dumazet <eduma...@google.com>; Nguyen, Anthony L
<anthony.l.ngu...@intel.com>; open list:NETWORKING DRIVERS
<net...@vger.kernel.org>; Jakub Kicinski <k...@kernel.org>; Paolo Abeni
<pab...@redhat.com>; David S. Miller <da...@davemloft.net>
Subject: Re: [Intel-wired-lan] [PATCH 1/2] igb: Disable threaded IRQ for
igb_msix_other
On 9/20/24 20:59, Wander Lairson Costa wrote:
> During testing of SR-IOV, Red Hat QE encountered an issue where the
> ip link up command intermittently fails for the igbvf interfaces when
> using the PREEMPT_RT variant. Investigation revealed that
> e1000_write_posted_mbx returns an error due to the lack of an ACK
> from e1000_poll_for_ack.
>
> The underlying issue arises from the fact that IRQs are threaded by
> default under PREEMPT_RT. While the exact hardware details are not
> available, it appears that the IRQ handled by igb_msix_other must
> be processed before e1000_poll_for_ack times out. However,
> e1000_write_posted_mbx is called with preemption disabled, leading
> to a scenario where the IRQ is serviced only after the failure of
> e1000_write_posted_mbx.
>
> To resolve this, we set IRQF_NO_THREAD for the affected interrupt,
> ensuring that the kernel handles it immediately, thereby preventing
> the aforementioned error.
>
> Reproducer:
>
> #!/bin/bash
>
> # echo 2 > /sys/class/net/ens14f0/device/sriov_numvfs
> ipaddr_vlan=3
> nic_test=ens14f0
> vf=${nic_test}v0
>
> while true; do
> ip link set ${nic_test} mtu 1500
> ip link set ${vf} mtu 1500
> ip link set $vf up
> ip link set ${nic_test} vf 0 vlan ${ipaddr_vlan}
> ip addr add 172.30.${ipaddr_vlan}.1/24 dev ${vf}
> ip addr add 2021:db8:${ipaddr_vlan}::1/64 dev ${vf}
> if ! ip link show $vf | grep 'state UP'; then
> echo 'Error found'
> break
> fi
> ip link set $vf down
> done
>
> Signed-off-by: Wander Lairson Costa <wan...@redhat.com>
> Reported-by: Yuying Ma <y...@redhat.com>
> ---
> drivers/net/ethernet/intel/igb/igb_main.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/net/ethernet/intel/igb/igb_main.c
> b/drivers/net/ethernet/intel/igb/igb_main.c
> index 1ef4cb871452..8a1696d7289f 100644
> --- a/drivers/net/ethernet/intel/igb/igb_main.c
> +++ b/drivers/net/ethernet/intel/igb/igb_main.c
> @@ -907,7 +907,7 @@ static int igb_request_msix(struct igb_adapter *adapter)
> int i, err = 0, vector = 0, free_vector = 0;
>
> err = request_irq(adapter->msix_entries[vector].vector,
> - igb_msix_other, 0, netdev->name, adapter);
> + igb_msix_other, IRQF_NO_THREAD, netdev->name,
> adapter);
> if (err)
> goto err_out;
>
Tested-by: Rafal Romanowski
<rafal.romanow...@intel.com<mailto:rafal.romanow...@intel.com>>
