Re: [PATCH v8 -tip 00/26] Core scheduling

[Ning, Hongyu]

On 2020/10/20 9:43, Joel Fernandes (Google) wrote:
> Eighth iteration of the Core-Scheduling feature.
> 
> Core scheduling is a feature that allows only 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). Core scheduling (as of v7) mitigates
> user-space to user-space attacks and user to kernel attack when one of
> the siblings enters the kernel via interrupts or system call.
> 
> 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 iteration focuses on the the following stuff:
> - Redesigned API.
> - Rework of Kernel Protection feature based on Thomas's entry work.
> - Rework of hotplug fixes.
> - Address review comments in v7
> 
> Joel: Both a CGroup and Per-task interface via prctl(2) are provided for
> configuring core sharing. More details are provided in documentation patch.
> Kselftests are provided to verify the correctness/rules of the interface.
> 
> Julien: TPCC tests showed improvements with core-scheduling. With kernel
> protection enabled, it does not show any regression. Possibly ASI will improve
> the performance for those who choose kernel protection (can be toggled through
> sched_core_protect_kernel sysctl). Results:
> v8				average		stdev		diff
> baseline (SMT on)		1197.272	44.78312824	
> core sched (   kernel protect)	412.9895	45.42734343	-65.51%
> core sched (no kernel protect)	686.6515	71.77756931	-42.65%
> nosmt				408.667		39.39042872	-65.87%
> 
> v8 is rebased on tip/master.
> 
> Future work
> ===========
> - Load balancing/Migration fixes for core scheduling.
>   With v6, Load balancing is partially coresched aware, but has some
>   issues w.r.t process/taskgroup weights:
>   https://lwn.net/ml/linux-kernel/20200225034438.GA617271@z...
> - Core scheduling test framework: kselftests, torture tests etc
> 
> Changes in v8
> =============
> - New interface/API implementation
>   - Joel
> - Revised kernel protection patch
>   - Joel
> - Revised Hotplug fixes
>   - Joel
> - Minor bug fixes and address review comments
>   - Vineeth
> 

> create mode 100644 tools/testing/selftests/sched/config
> create mode 100644 tools/testing/selftests/sched/test_coresched.c
> 

Adding 4 workloads test results for Core Scheduling v8: 

- kernel under test: coresched community v8 from https://git.kernel.org/pub/scm/linux/kernel/git/jfern/linux.git/log/?h=coresched-v5.9
- workloads: 
	-- A. sysbench cpu (192 threads) + sysbench cpu (192 threads)
	-- B. sysbench cpu (192 threads) + sysbench mysql (192 threads, mysqld forced into the same cgroup)
	-- C. uperf netperf.xml (192 threads over TCP or UDP protocol separately)
	-- D. will-it-scale context_switch via pipe (192 threads)
- test machine setup: 
	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
- test results:
	-- workload A, no obvious performance drop in cs_on:
	+----------------------+------+----------------------+------------------------+
	|                      | **   | sysbench cpu * 192   | sysbench mysql * 192   |
	+======================+======+======================+========================+
	| cgroup               | **   | cg_sysbench_cpu_0    | cg_sysbench_mysql_0    |
	+----------------------+------+----------------------+------------------------+
	| record_item          | **   | Tput_avg (events/s)  | Tput_avg (events/s)    |
	+----------------------+------+----------------------+------------------------+
	| coresched_normalized | **   | 1.01                 | 0.87                   |
	+----------------------+------+----------------------+------------------------+
	| default_normalized   | **   | 1                    | 1                      |
	+----------------------+------+----------------------+------------------------+
	| smtoff_normalized    | **   | 0.59                 | 0.82                   |
	+----------------------+------+----------------------+------------------------+

	-- workload B, no obvious performance drop in cs_on:
	+----------------------+------+----------------------+------------------------+
	|                      | **   | sysbench cpu * 192   | sysbench cpu * 192     |
	+======================+======+======================+========================+
	| cgroup               | **   | cg_sysbench_cpu_0    | cg_sysbench_cpu_1      |
	+----------------------+------+----------------------+------------------------+
	| record_item          | **   | Tput_avg (events/s)  | Tput_avg (events/s)    |
	+----------------------+------+----------------------+------------------------+
	| coresched_normalized | **   | 1.01                 | 0.98                   |
	+----------------------+------+----------------------+------------------------+
	| default_normalized   | **   | 1                    | 1                      |
	+----------------------+------+----------------------+------------------------+
	| smtoff_normalized    | **   | 0.6                  | 0.6                    |
	+----------------------+------+----------------------+------------------------+

	-- workload C, known performance drop in cs_on since Core Scheduling v6:
	+----------------------+------+---------------------------+---------------------------+
	|                      | **   | uperf netperf TCP * 192   | uperf netperf UDP * 192   |
	+======================+======+===========================+===========================+
	| cgroup               | **   | cg_uperf                  | cg_uperf                  |
	+----------------------+------+---------------------------+---------------------------+
	| record_item          | **   | Tput_avg (Gb/s)           | Tput_avg (Gb/s)           |
	+----------------------+------+---------------------------+---------------------------+
	| coresched_normalized | **   | 0.46                      | 0.48                      |
	+----------------------+------+---------------------------+---------------------------+
	| default_normalized   | **   | 1                         | 1                         |
	+----------------------+------+---------------------------+---------------------------+
	| smtoff_normalized    | **   | 0.82                      | 0.79                      |
	+----------------------+------+---------------------------+---------------------------+

	-- workload D, new added syscall workload, performance drop in cs_on:
	+----------------------+------+-------------------------------+
	|                      | **   | will-it-scale  * 192          |
	|                      |      | (pipe based context_switch)   |
	+======================+======+===============================+
	| cgroup               | **   | cg_will-it-scale              |
	+----------------------+------+-------------------------------+
	| record_item          | **   | threads_avg                   |
	+----------------------+------+-------------------------------+
	| coresched_normalized | **   | 0.2                           |
	+----------------------+------+-------------------------------+
	| default_normalized   | **   | 1                             |
	+----------------------+------+-------------------------------+
	| smtoff_normalized    | **   | 0.89                          |
	+----------------------+------+-------------------------------+

	comments: per internal analyzing, suspected huge amount of spin_lock contention in cs_on, may lead to significant performance drop

- notes on test results record_item:
	* coresched_normalized: smton, cs enabled, test result normalized by default value
	* default_normalized: smton, cs disabled, test result normalized by default value
	* smtoff_normalized: smtoff, test result normalized by default value