[PATCH] Revert "iommu/arm-smmu-v3: Decrease the queue size of evtq and priq"

[Robin Murphy]

On 2021-12-14 14:48, Will Deacon wrote:
> On Tue, Dec 07, 2021 at 02:32:48PM +0800, Zhou Wang wrote:
>> The commit f115f3c0d5d8 ("iommu/arm-smmu-v3: Decrease the queue size of
>> evtq and priq") decreases evtq and priq, which may lead evtq/priq to be
>> full with fault events, e.g HiSilicon ZIP/SEC/HPRE have maximum 1024 queues
>> in one device, every queue could be binded with one process and trigger a
>> fault event. So let's revert f115f3c0d5d8.
>>
>> In fact, if an implementation of SMMU really does not need so long evtq
>> and priq, value of IDR1_EVTQS and IDR1_PRIQS can be set to proper ones.
>>
>> Signed-off-by: Zhou Wang <wangzhou1 at hisilicon.com>
>> ---
>>   drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h | 5 ++---
>>   1 file changed, 2 insertions(+), 3 deletions(-)
> 
> I'd like an Ack from Zhen Lei on this, as the aim of the original patch
> was to reduce memory consumption.

I wonder if it's time to start trying to be a bit cleverer than just 
allocating the smallest/largest possible queues, and try to scale them 
to some heuristic of the "size" of the system? Certainly a module 
parameter so that users can manually tune for their system/workload 
might be a reasonable compromise.

I'm also tempted by the idea of trying to dynamically reallocate larger 
queues if they fill up, but I guess that depends on whether it's already 
game over if events or PRI requests are lost...

Robin.