Re: [PATCH 1/2] iommu/arm-smmu-v3: Replace sort_nonatomic() with sort()

On 02/08/2026 6:45 pm, Nicolin Chen wrote:
> On Sun, Aug 02, 2026 at 10:23:48AM +0100, Will Deacon wrote:
>> On Thu, Jul 30, 2026 at 06:12:15PM +0000, Kuan-Wei Chiu wrote:
>>> @@ -4047,9 +4047,9 @@ static int arm_smmu_insert_master(struct arm_smmu_device *smmu,
>>>   	}
>>>   
>>>   	/* Put the ids into order for sorted to_merge/to_unref arrays */
>>> -	sort_nonatomic(master->streams, master->num_streams,
>>> -		       sizeof(master->streams[0]), arm_smmu_stream_id_cmp,
>>> -		       NULL);
>>> +	sort(master->streams, master->num_streams,
>>> +	     sizeof(master->streams[0]), arm_smmu_stream_id_cmp,
>>> +	     NULL);
>>
>> Makes sense to me. Nicolin, did you choose the nonatomic version
>> specifically?
> 
> It's probably rare to have a large multi-stream array, so I think
> sort() would be fine.

Yeah, probably 99% of the time the size of this array will be 1. An 
exceptional value of "large" might be something like 64 for a massive 
(non-PCI) DMA engine with separate read and write IDs per channel for no 
good reason.

If and when someone ever were to report RCU stalls here then we can 
first ask them what the heck their client device is... and unless and 
until then I wouldn't think it's worth worrying about.

Thanks,
Robin.