Re: [RFC PATCH 00/13] Core scheduling v5

[Ning, Hongyu]

- Test environment:
Intel Xeon Server platform
CPU(s):              192
On-line CPU(s) list: 0-191
Thread(s) per core:  2
Core(s) per socket:  48
Socket(s):           2
NUMA node(s):        4

- Kernel under test: 
Core scheduling v5 base
https://github.com/digitalocean/linux-coresched/tree/coresched/v5-v5.5.y

- Test set based on sysbench 1.1.0-bd4b418:
A: sysbench cpu in cgroup cpu 1 + sysbench mysql in cgroup mysql 1 (192 workload tasks for each cgroup)
B: sysbench cpu in cgroup cpu 1 + sysbench cpu in cgroup cpu 2 + sysbench mysql in cgroup mysql 1 + sysbench mysql in cgroup mysql 2 (192 workload tasks for each cgroup)

- Test results briefing:
1 Good results:
1.1 For test set A, coresched could achieve same or better performance compared to smt_off, for both cpu workload and sysbench workload
1.2 For test set B, cpu workload, coresched could achieve better performance compared to smt_off

2 Bad results:
2.1 For test set B, mysql workload, coresched performance is lower than smt_off, potential fairness issue between cpu workloads and mysql workloads
2.2 For test set B, cpu workload, potential fairness issue between 2 cgroups cpu workloads

- Test results:
Note: test results in following tables are Tput normalized to default baseline

-- Test set A Tput normalized results:
+--------------------+--------+-----------+-------------+-----------+-------+-------------+---------------+-------------+
|                    | ****   | default   | coresched   | smt_off   | ***   | default     | coresched     | smt_off     |
+====================+========+===========+=============+===========+=======+=============+===============+=============+
| cgroups            | ****   | cg cpu 1  | cg cpu 1    | cg cpu 1  | ***   | cg mysql 1  | cg mysql 1    | cg mysql 1  |
+--------------------+--------+-----------+-------------+-----------+-------+-------------+---------------+-------------+
| sysbench workload  | ****   | cpu       | cpu         | cpu       | ***   | mysql       | mysql         | mysql       |
+--------------------+--------+-----------+-------------+-----------+-------+-------------+---------------+-------------+
| 192 tasks / cgroup | ****   | 1         | 0.95        | 0.54      | ***   | 1           | 0.92          | 0.97        |
+--------------------+--------+-----------+-------------+-----------+-------+-------------+---------------+-------------+

-- Test set B Tput normalized results:
+--------------------+--------+-----------+-------------+-----------+-------+-------------+---------------+-------------+------+-------------+---------------+-------------+-----+-------------+---------------+-------------+
|                    | ****   | default   | coresched   | smt_off   | ***   | default     | coresched     | smt_off     | **   | default     | coresched     | smt_off     | *   | default     | coresched     | smt_off     |
+====================+========+===========+=============+===========+=======+=============+===============+=============+======+=============+===============+=============+=====+=============+===============+=============+
| cgroups            | ****   | cg cpu 1  | cg cpu 1    | cg cpu 1  | ***   | cg cpu 2    | cg cpu 2      | cg cpu 2    | **   | cg mysql 1  | cg mysql 1    | cg mysql 1  | *   | cg mysql 2  | cg mysql 2    | cg mysql 2  |
+--------------------+--------+-----------+-------------+-----------+-------+-------------+---------------+-------------+------+-------------+---------------+-------------+-----+-------------+---------------+-------------+
| sysbench workload  | ****   | cpu       | cpu         | cpu       | ***   | cpu         | cpu           | cpu         | **   | mysql       | mysql         | mysql       | *   | mysql       | mysql         | mysql       |
+--------------------+--------+-----------+-------------+-----------+-------+-------------+---------------+-------------+------+-------------+---------------+-------------+-----+-------------+---------------+-------------+
| 192 tasks / cgroup | ****   | 1         | 0.9         | 0.47      | ***   | 1           | 1.32          | 0.66        | **   | 1           | 0.42          | 0.89        | *   | 1           | 0.42          | 0.89        |
+--------------------+--------+-----------+-------------+-----------+-------+-------------+---------------+-------------+------+-------------+---------------+-------------+-----+-------------+---------------+-------------+


> On Date: Wed,  4 Mar 2020 16:59:50 +0000, vpillai <vpillai@xxxxxxxxxxxxxxxx> wrote:
> To: Nishanth Aravamudan <naravamudan@xxxxxxxxxxxxxxxx>, Julien Desfossez <jdesfossez@xxxxxxxxxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>, mingo@xxxxxxxxxx, tglx@xxxxxxxxxxxxx, pjt@xxxxxxxxxx, torvalds@xxxxxxxxxxxxxxxxxxxx
> CC: vpillai <vpillai@xxxxxxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, fweisbec@xxxxxxxxx, keescook@xxxxxxxxxxxx, kerrnel@xxxxxxxxxx, Phil Auld <pauld@xxxxxxxxxx>, Aaron Lu <aaron.lwe@xxxxxxxxx>, Aubrey Li <aubrey.intel@xxxxxxxxx>, aubrey.li@xxxxxxxxxxxxxxx, Valentin Schneider <valentin.schneider@xxxxxxx>, Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>, Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>, Paolo Bonzini <pbonzini@xxxxxxxxxx>, Joel Fernandes <joelaf@xxxxxxxxxx>, joel@xxxxxxxxxxxxxxxxx
> 
> 
> Fifth iteration of the Core-Scheduling feature.
> 
> Core scheduling is a feature that only allows trusted tasks to run
> concurrently on cpus sharing compute resources(eg: hyperthreads on a
> core). The goal is to mitigate the core-level side-channel attacks
> without requiring to disable SMT (which has a significant impact on
> performance in some situations). So far, the feature mitigates user-space
> to user-space attacks but not user-space to kernel attack, when one of
> the hardware thread enters the kernel (syscall, interrupt etc).
> 
> By default, the feature doesn't change any of the current scheduler
> behavior. The user decides which tasks can run simultaneously on the
> same core (for now by having them in the same tagged cgroup). When
> a tag is enabled in a cgroup and a task from that cgroup is running
> on a hardware thread, the scheduler ensures that only idle or trusted
> tasks run on the other sibling(s). Besides security concerns, this
> feature can also be beneficial for RT and performance applications
> where we want to control how tasks make use of SMT dynamically.
> 
> This version was focusing on performance and stability. Couple of
> crashes related to task tagging and cpu hotplug path were fixed.
> This version also improves the performance considerably by making
> task migration and load balancing coresched aware.
> 
> In terms of performance, the major difference since the last iteration
> is that now even IO-heavy and mixed-resources workloads are less
> impacted by core-scheduling than by disabling SMT. Both host-level and
> VM-level benchmarks were performed. Details in:
> https://lkml.org/lkml/2020/2/12/1194
> https://lkml.org/lkml/2019/11/1/269
> 
> v5 is rebased on top of 5.5.5(449718782a46)
> https://github.com/digitalocean/linux-coresched/tree/coresched/v5-v5.5.y
>