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 d34c54d173 ("i40e: Use
irq_update_affinity_hint()").
[1] https://github.com/Irqbalance/irqbalance/commit/dcc411e7bfdd
Signed-off-by: Michal Schmidt <mschmidt@redhat.com>
Reviewed-by: Sunil Goutham <sgoutham@marvell.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Pucha Himasekhar Reddy <himasekharx.reddy.pucha@intel.com>
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://lore.kernel.org/r/20240607-next-2024-06-03-intel-next-batch-v3-3-d1470cee3347@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
dee55767dc