Re: [PATCH 3/3] iommu/vt-d: Size Page Request Queue to avoid overflow condition

Lu Baolu
2022-04-18T11:44:51Z

On 2022/4/18 15:00, Tian, Kevin wrote:
>> From: Lu Baolu<baolu.lu@linux.intel.com>
>> Sent: Saturday, April 16, 2022 8:31 PM
>>
>> PRQ overflow may cause I/O throughput congestion, resulting in unnecessary
>> degradation of IO performance. Appropriately increasing the length of PRQ
>> can greatly reduce the occurrence of PRQ overflow. The count of maximum
>> page requests that can be generated in parallel by a PCIe device is
>> statically defined in the Outstanding Page Request Capacity field of the
>> PCIe ATS configure space.
>>
>> The new lenght of PRQ is calculated by summing up the value of Outstanding
>> Page Request Capacity register across all devices where Page Requests are
>> supported on the real PR-capable platfrom (Intel Sapphire Rapids). The
>> result is round to the nearest higher power of 2.
> The actual requirement is usage and platform specific. What about
> doubling the default size and also provide an option for admin to
> tune?

I also have this in my list to provide an opt-in interface for user. But
I don't want to include it in this series as this is only for small
tuning. The opt-in interface looks more like a new feature. :-)

Best regards,
baolu