Re: [RFC PATCH v4 00/19] Core scheduling v4

[Tim Chen]

On 11/11/19 11:10 AM, Tim Chen wrote:
> On 10/30/19 11:33 AM, Vineeth Remanan Pillai wrote:
>> Fourth iteration of the Core-Scheduling feature.
>>
>> This version was aiming mostly at addressing the vruntime comparison
>> issues with v3. The main issue seen in v3 was the starvation of
>> interactive tasks when competing with cpu intensive tasks. This issue
>> is mitigated to a large extent.
>>
>> We have tested and verified that incompatible processes are not
>> selected during schedule. In terms of performance, the impact
>> depends on the workload:
>> - on CPU intensive applications that use all the logical CPUs with
>>   SMT enabled, enabling core scheduling performs better than nosmt.
>> - on mixed workloads with considerable io compared to cpu usage,
>>   nosmt seems to perform better than core scheduling.
>>
>> v4 is rebased on top of 5.3.5(dc073f193b70):
>> https://github.com/digitalocean/linux-coresched/tree/coresched/v4-v5.3.5
>>
> 
> The v4 core scheduler will crash when you toggle the core scheduling
> tag of the cgroup while there are active tasks in the cgroup running.
> 
> The reason is because we don't properly move tasks in and out of the
> core scheduler queue according to the new core scheduling tag status.
> A task's core scheduler status will then get misaligned with its core
> cookie status.
> 
> The patch below fixes that.
> 
> Thanks.
> 
> Tim
> 

I also encountered kernel panic with the v4 code when taking cpu offline or online
when core scheduler is running.  I've refreshed the previous patch, along
with 3 other patches to fix problems related to CPU online/offline.

As a side effect of the fix, each core can now operate in core-scheduling
mode or non core-scheduling mode, depending on how many online SMT threads it has.

Vineet, are you guys planning to refresh v4 and update it to v5?  Aubrey posted
a port to the latest kernel earlier.

Tim

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