netdev - [PATCH v3 3/3] ice: use irq_update_affinity

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Message-Id: <20240607-next-2024-06-03-intel-next-batch-v3-3-d1470cee3347@intel.com>
Date: Fri, 07 Jun 2024 14:22:34 -0700
From: Jacob Keller <jacob.e.keller@...el.com>
To: Jakub Kicinski <kuba@...nel.org>, David Miller <davem@...emloft.net>, 
 netdev <netdev@...r.kernel.org>
Cc: Jacob Keller <jacob.e.keller@...el.com>, 
 Michal Schmidt <mschmidt@...hat.com>, Sunil Goutham <sgoutham@...vell.com>, 
 Pucha Himasekhar Reddy <himasekharx.reddy.pucha@...el.com>
Subject: [PATCH v3 3/3] ice: use irq_update_affinity_hint()

From: Michal Schmidt <mschmidt@...hat.com>

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>
Reviewed-by: Sunil Goutham <sgoutham@...vell.com>
Reviewed-by: Jacob Keller <jacob.e.keller@...el.com>
Tested-by: Pucha Himasekhar Reddy <himasekharx.reddy.pucha@...el.com>
Signed-off-by: Jacob Keller <jacob.e.keller@...el.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 7629b0190578..f559e60992fa 100644
--- a/drivers/net/ethernet/intel/ice/ice_lib.c
+++ b/drivers/net/ethernet/intel/ice/ice_lib.c
@@ -2580,8 +2580,8 @@ 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 1b61ca3a6eb6..7d9a4e856f61 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;

-- 
2.44.0.53.g0f9d4d28b7e6