netdev - [PATCH iwl-next] ice: use irq_update_affinity

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Message-ID: <20240522231256.587985-1-mschmidt@redhat.com>
Date: Thu, 23 May 2024 01:12:56 +0200
From: Michal Schmidt <mschmidt@...hat.com>
To: Jesse Brandeburg <jesse.brandeburg@...el.com>,
	Tony Nguyen <anthony.l.nguyen@...el.com>,
	intel-wired-lan@...ts.osuosl.org
Cc: netdev@...r.kernel.org,
	Nitesh Narayan Lal <nitesh@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH iwl-next] ice: use irq_update_affinity_hint()

irq_set_affinity_hint() is deprecated. Use irq_update_affinity_hint()
instead. This removes the side-effect of actually applying the affinity.

The driver does not really need to worry about spreading its IRQs across
CPUs. The core code already takes care of that.
On the contrary, when the driver applies affinities by itself, it breaks
the users' expectations:
 1. The user configures irqbalance with IRQBALANCE_BANNED_CPULIST in
    order to prevent IRQs from being moved to certain CPUs that run a
    real-time workload.
 2. ice reconfigures VSIs at runtime due to a MIB change
    (ice_dcb_process_lldp_set_mib_change). Reopening a VSI resets the
    affinity in ice_vsi_req_irq_msix().
 3. ice has no idea about irqbalance's config, so it may move an IRQ to
    a banned CPU. The real-time workload suffers unacceptable latency.

I am not sure if updating the affinity hints is at all useful, because
irqbalance ignores them since 2016 ([1]), but at least it's harmless.

This ice change is similar to i40e commit d34c54d1739c ("i40e: Use
irq_update_affinity_hint()").

[1] https://github.com/Irqbalance/irqbalance/commit/dcc411e7bfdd

Signed-off-by: Michal Schmidt <mschmidt@...hat.com>
---
 drivers/net/ethernet/intel/ice/ice_lib.c  | 4 ++--
 drivers/net/ethernet/intel/ice/ice_main.c | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/intel/ice/ice_lib.c b/drivers/net/ethernet/intel/ice/ice_lib.c
index 5371e91f6bbb..0f8b622db2b5 100644
--- a/drivers/net/ethernet/intel/ice/ice_lib.c
+++ b/drivers/net/ethernet/intel/ice/ice_lib.c
@@ -2587,8 +2587,8 @@ void ice_vsi_free_irq(struct ice_vsi *vsi)
 		if (!IS_ENABLED(CONFIG_RFS_ACCEL))
 			irq_set_affinity_notifier(irq_num, NULL);
 
-		/* clear the affinity_mask in the IRQ descriptor */
-		irq_set_affinity_hint(irq_num, NULL);
+		/* clear the affinity_hint in the IRQ descriptor */
+		irq_update_affinity_hint(irq_num, NULL);
 		synchronize_irq(irq_num);
 		devm_free_irq(ice_pf_to_dev(pf), irq_num, vsi->q_vectors[i]);
 	}
diff --git a/drivers/net/ethernet/intel/ice/ice_main.c b/drivers/net/ethernet/intel/ice/ice_main.c
index f60c022f7960..a5d369b8fed5 100644
--- a/drivers/net/ethernet/intel/ice/ice_main.c
+++ b/drivers/net/ethernet/intel/ice/ice_main.c
@@ -2607,7 +2607,7 @@ static int ice_vsi_req_irq_msix(struct ice_vsi *vsi, char *basename)
 		}
 
 		/* assign the mask for this irq */
-		irq_set_affinity_hint(irq_num, &q_vector->affinity_mask);
+		irq_update_affinity_hint(irq_num, &q_vector->affinity_mask);
 	}
 
 	err = ice_set_cpu_rx_rmap(vsi);
@@ -2625,7 +2625,7 @@ static int ice_vsi_req_irq_msix(struct ice_vsi *vsi, char *basename)
 		irq_num = vsi->q_vectors[vector]->irq.virq;
 		if (!IS_ENABLED(CONFIG_RFS_ACCEL))
 			irq_set_affinity_notifier(irq_num, NULL);
-		irq_set_affinity_hint(irq_num, NULL);
+		irq_update_affinity_hint(irq_num, NULL);
 		devm_free_irq(dev, irq_num, &vsi->q_vectors[vector]);
 	}
 	return err;
-- 
2.44.0