Re: [PATCH v5 2/2] sched/numa: add statistics of numa balance task

["Chen, Yu C" <yu.c.chen@intel.com>]

On 5/28/2025 1:48 AM, Shakeel Butt wrote:
> On Sun, May 25, 2025 at 08:35:24PM +0800, Chen, Yu C wrote:
>> On 5/25/2025 1:32 AM, Shakeel Butt wrote:
> [...]
>>> can you please give an end-to-end> flow/story of all these events
>> happening on a timeline.
>>>
>>
>> Yes, sure, let me have a try.
>>
>> The goal of NUMA balancing is to co-locate a task and its
>> memory pages on the same NUMA node. There are two strategies:
>> migrate the pages to the task's node, or migrate the task to
>> the node where its pages reside.
>>
>> Suppose a task p1 is running on Node 0, but its pages are
>> located on Node 1. NUMA page fault statistics for p1 reveal
>> its "page footprint" across nodes. If NUMA balancing detects
>> that most of p1's pages are on Node 1:
>>
>> 1.Page Migration Attempt:
>> The Numa balance first tries to migrate p1's pages to Node 0.
>> The numa_page_migrate counter increments.
>>
>> 2.Task Migration Strategies:
>> After the page migration finishes, Numa balance checks every
>> 1 second to see if p1 can be migrated to Node 1.
>>
>> Case 2.1: Idle CPU Available
>> If Node 1 has an idle CPU, p1 is directly scheduled there. This event is
>> logged as numa_task_migrated.
>> Case 2.2: No Idle CPU (Task Swap)
>> If all CPUs on Node1 are busy, direct migration could cause CPU contention
>> or load imbalance. Instead:
>> The Numa balance selects a candidate task p2 on Node 1 that prefers
>> Node 0 (e.g., due to its own page footprint).
>> p1 and p2 are swapped. This cross-node swap is recorded as
>> numa_task_swapped.
>>
> 
> Thanks for the explanation, this is really helpful and I would like this
> to be included in the commit message.
> 

OK, just sent out a v6 with the commit message enhanced.

Thanks,
Chenyu