netdev - Re: [Intel-wired-lan] [PATCH iwl-next v1] ice: lower default irq/queue counts on high-core systems

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Message-ID: <34268765-6cc5-4816-9ba7-4f00e8f353a0@intel.com>
Date: Fri, 17 Oct 2025 07:03:31 +0200
From: Przemek Kitszel <przemyslaw.kitszel@...el.com>
To: Alexander Lobakin <aleksander.lobakin@...el.com>, Michal Swiatkowski
	<michal.swiatkowski@...ux.intel.com>
CC: <intel-wired-lan@...ts.osuosl.org>, <netdev@...r.kernel.org>, Jacob Keller
	<jacob.e.keller@...el.com>
Subject: Re: [Intel-wired-lan] [PATCH iwl-next v1] ice: lower default
 irq/queue counts on high-core systems

On 10/16/25 17:36, Alexander Lobakin wrote:
> From: Michal Swiatkowski <michal.swiatkowski@...ux.intel.com>
> Date: Thu, 16 Oct 2025 08:22:50 +0200
> 
>> On some high-core systems loading ice driver with default values can
>> lead to queue/irq exhaustion. It will result in no additional resources
>> for SR-IOV.
>>
>> In most cases there is no performance reason for more than 64 queues.
>> Limit the default value to 64. Still, using ethtool the number of
>> queues can be changed up to num_online_cpus().
>>
>> This change affects only the default queue amount on systems with more
>> than 64 cores.
>>
>> Reviewed-by: Jacob Keller <jacob.e.keller@...el.com>
>> Signed-off-by: Michal Swiatkowski <michal.swiatkowski@...ux.intel.com>
>> ---
>>   drivers/net/ethernet/intel/ice/ice.h     | 20 ++++++++++++++++++++
>>   drivers/net/ethernet/intel/ice/ice_irq.c |  6 ++++--
>>   drivers/net/ethernet/intel/ice/ice_lib.c |  8 ++++----
>>   3 files changed, 28 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/intel/ice/ice.h b/drivers/net/ethernet/intel/ice/ice.h
>> index 3d4d8b88631b..354ec2950ff3 100644
>> --- a/drivers/net/ethernet/intel/ice/ice.h
>> +++ b/drivers/net/ethernet/intel/ice/ice.h
>> @@ -1133,4 +1133,24 @@ static inline struct ice_hw *ice_get_primary_hw(struct ice_pf *pf)
>>   	else
>>   		return &pf->adapter->ctrl_pf->hw;
>>   }
>> +
>> +/**
>> + * ice_capped_num_cpus - normalize the number of CPUs to a reasonable limit
>> + *
>> + * This function returns the number of online CPUs, but caps it at suitable
>> + * default to prevent excessive resource allocation on systems with very high
>> + * CPU counts.
>> + *
>> + * Note: suitable default is currently at 64, which is reflected in default_cpus
>> + * constant. In most cases there is no much benefit for more than 64 and it is a
>> + * power of 2 number.
>> + *
>> + * Return: number of online CPUs, capped at suitable default.
>> + */
>> +static inline u16 ice_capped_num_cpus(void)
>> +{
>> +	const int default_cpus = 64;
> 
> Maybe we should just use netif_get_num_default_rss_queues() like I did
> in idpf?
> 
> Or it still can be too high e.g. on clusters with > 256 CPUs?

good point,
perhaps we should both use it and change the (kernel) func to cap at 64

> 
>> +
>> +	return min(num_online_cpus(), default_cpus);
>> +}
>>   #endif /* _ICE_H_ */
> Thanks,
> Olek
>