On 09/02/21 00:12, Song Bao Hua (Barry Song) wrote:
-----Original Message----- From: Valentin Schneider [mailto:valentin.schneider@arm.com]
Yes; let's take your topology for instance:
node 0 1 2 3 0: 10 12 20 22 1: 12 10 22 24 2: 20 22 10 12 3: 22 24 12 10
2 10 20 <---> 1 <---> 2 <---> 3
Guess you actually mean 2 10 2 1 <---> 0 <---> 2 <---> 3
Yeah, you're right, sorry about that!
Domains for node1 will look like (before any fixes are applied):
NUMA<=10: span=1 groups=(1) NUMA<=12: span=0-1 groups=(1)->(0) NUMA<=20: span=0-1 groups=(0,1) NUMA<=22: span=0-2 groups=(0,1)->(0,2-3) NUMA<=24: span=0-3 groups=(0-2)->(0,2-3)
As you can see, the domain representing distance <= 20 will be degenerated (it has a single group). If we were to e.g. add some more nodes to the left of node0, then we would trigger the "grandchildren logic" for node1 and would end up creating a reference to node1 NUMA<=20's sgc, which is a mistake: that domain will be degenerated, and that sgc will never be updated. The right thing to do here would be reference node1 NUMA<=12's sgc, which the above snippet does.
Guess I got your point even though the diagram is not correct :-)
Good!
If the topology is as below(add a node left to node1 rather than node0):
9 2 10 2A <---> 1 <---> 0 <---> 2 <---> 3
For nodeA, NUMA<=10: span=A groups=(A) NUMA<=12: span= A groups= (A) NUMA<=19: span=A-1 groups=(A),(1) NUMA<=20: span=A-1 groups=(A,1) *1 NUMA<=21: span=A-1-0 groups=(A,1), node1's numa<=20
For node0, NUMA<=10: span=9 groups=(0) #3 NUMA<=12: span=0-1 groups=(0)->(1) #2 NUMA<=19: span=0-1 groups=(0,1) #1 NUMA<=20: span=0-1-2 groups=(0,1),....
*1 will firstly try #1, and it finds 2 is outside the A-1-0, then it will try #2. Finally #2 will be degenerated, so we should actually use #3. Amazing!
Bingo!
- return parent;
+}
Thanks Barry