On 2020/4/15 17:30, Tian, Kevin wrote:
From: Lu Baolu<baolu.lu@xxxxxxxxxxxxxxx>I may overlook something but isn't the prq interrupt thread
Sent: Wednesday, April 15, 2020 1:26 PM
Currently, the page request interrupt thread handles the page
requests in the queue in this way:
- Clear PPR bit to ensure new interrupt could come in;
- Read and record the head and tail registers;
- Handle all descriptors between head and tail;
- Write tail to head register.
This might cause some descriptors to be handles multiple times.
An example sequence:
- Thread A got scheduled with PRQ_1 and PRQ_2 in the queue;
- Thread A clear the PPR bit and record the head and tail;
- A new PRQ_3 comes and Thread B gets scheduled;
- Thread B record the head and tail which includes PRQ_1
ÂÂ and PRQ_2.
per iommu then why would two prq threads contend here?
The prq interrupt could be masked by the PPR (Pending Page Request) bit
in Page Request Status Register. In the interrupt handling thread once
this bit is clear, new prq interrupts are allowed to be generated.
So, if a page request is in process and the PPR bit is cleared, another
page request from any devices under the same iommu could trigger another
interrupt thread.