Messages in this thread | | | From | Valentin Schneider <> | Subject | RE: [RFC PATCH 1/2] sched/topology: Get rid of NUMA overlapping groups | Date | Tue, 09 Feb 2021 10:41:45 +0000 |
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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 2 >> 0 <---> 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 2 > A <---> 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
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