Re: [PATCH -tip 00/32] Core scheduling (v9)

[Vincent Guittot <vincent.guittot@linaro.org>]

Hi Joel,

On Wed, 18 Nov 2020 at 00:20, Joel Fernandes (Google)
<joel@joelfernandes.org> wrote:
>
> Core-Scheduling
> ===============
> Enclosed is series v9 of core scheduling.
> v9 is rebased on tip/master (fe4adf6f92c4 ("Merge branch 'irq/core'"))..
> I hope that this version is acceptable to be merged (pending any new review

./scripts/get_maintainer.pl is quite useful to make sure that all
maintainers are cced and helps a lot to get some reviews

> comments that arise) as the main issues in the past are all resolved:
>  1. Vruntime comparison.
>  2. Documentation updates.
>  3. CGroup and per-task interface developed by Google and Oracle.
>  4. Hotplug fixes.
> Almost all patches also have Reviewed-by or Acked-by tag. See below for full
> list of changes in v9.
>
> Introduction of 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.
>
> 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.
>
> Testing
> =======
> ChromeOS testing shows 300% improvement in keypress latency on a Google
> docs key press with Google hangout test (the maximum latency drops from 150ms
> to 50ms for keypresses).
>
> Julien: TPCC tests showed improvements with core-scheduling as below. 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).
>                                 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%
> (Note these results are from v8).
>
> Vineeth tested sysbench and does not see any regressions.
> Hong and Aubrey tested v9 and see results similar to v8. There is a known issue
> with uperf that does regress. This appears to be because of ksoftirq heavily
> contending with other tasks on the core. The consensus is this can be improved
> in the future.
>
> Changes in v9
> =============
> - Note that the vruntime snapshot change is written in 2 patches to show the
>   progression of the idea and prevent merge conflicts:
>     sched/fair: Snapshot the min_vruntime of CPUs on force idle
>     sched: Improve snapshotting of min_vruntime for CGroups
>   Same with the RT priority inversion change:
>     sched: Fix priority inversion of cookied task with sibling
>     sched: Improve snapshotting of min_vruntime for CGroups
> - Disable coresched on certain AMD HW.
>
> 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
>
> Changes in v7
> =============
> - Kernel protection from untrusted usermode tasks
>   - Joel, Vineeth
> - Fix for hotplug crashes and hangs
>   - Joel, Vineeth
>
> Changes in v6
> =============
> - Documentation
>   - Joel
> - Pause siblings on entering nmi/irq/softirq
>   - Joel, Vineeth
> - Fix for RCU crash
>   - Joel
> - Fix for a crash in pick_next_task
>   - Yu Chen, Vineeth
> - Minor re-write of core-wide vruntime comparison
>   - Aaron Lu
> - Cleanup: Address Review comments
> - Cleanup: Remove hotplug support (for now)
> - Build fixes: 32 bit, SMT=n, AUTOGROUP=n etc
>   - Joel, Vineeth
>
> Changes in v5
> =============
> - Fixes for cgroup/process tagging during corner cases like cgroup
>   destroy, task moving across cgroups etc
>   - Tim Chen
> - Coresched aware task migrations
>   - Aubrey Li
> - Other minor stability fixes.
>
> Changes in v4
> =============
> - Implement a core wide min_vruntime for vruntime comparison of tasks
>   across cpus in a core.
>   - Aaron Lu
> - Fixes a typo bug in setting the forced_idle cpu.
>   - Aaron Lu
>
> Changes in v3
> =============
> - Fixes the issue of sibling picking up an incompatible task
>   - Aaron Lu
>   - Vineeth Pillai
>   - Julien Desfossez
> - Fixes the issue of starving threads due to forced idle
>   - Peter Zijlstra
> - Fixes the refcounting issue when deleting a cgroup with tag
>   - Julien Desfossez
> - Fixes a crash during cpu offline/online with coresched enabled
>   - Vineeth Pillai
> - Fixes a comparison logic issue in sched_core_find
>   - Aaron Lu
>
> Changes in v2
> =============
> - Fixes for couple of NULL pointer dereference crashes
>   - Subhra Mazumdar
>   - Tim Chen
> - Improves priority comparison logic for process in different cpus
>   - Peter Zijlstra
>   - Aaron Lu
> - Fixes a hard lockup in rq locking
>   - Vineeth Pillai
>   - Julien Desfossez
> - Fixes a performance issue seen on IO heavy workloads
>   - Vineeth Pillai
>   - Julien Desfossez
> - Fix for 32bit build
>   - Aubrey Li
>
> 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...
>
> Aubrey Li (1):
> sched: migration changes for core scheduling
>
> Joel Fernandes (Google) (16):
> sched/fair: Snapshot the min_vruntime of CPUs on force idle
> sched: Enqueue task into core queue only after vruntime is updated
> sched: Simplify the core pick loop for optimized case
> sched: Improve snapshotting of min_vruntime for CGroups
> arch/x86: Add a new TIF flag for untrusted tasks
> kernel/entry: Add support for core-wide protection of kernel-mode
> entry/idle: Enter and exit kernel protection during idle entry and
> exit
> sched: Split the cookie and setup per-task cookie on fork
> sched: Add a per-thread core scheduling interface
> sched: Release references to the per-task cookie on exit
> sched/debug: Add CGroup node for printing group cookie if SCHED_DEBUG
> kselftest: Add tests for core-sched interface
> sched: Move core-scheduler interfacing code to a new file
> Documentation: Add core scheduling documentation
> sched: Add a coresched command line option
> sched: Debug bits...
>
> Josh Don (2):
> sched: Refactor core cookie into struct
> sched: Add a second-level tag for nested CGroup usecase
>
> Peter Zijlstra (11):
> sched: Wrap rq::lock access
> sched: Introduce sched_class::pick_task()
> sched/fair: Fix pick_task_fair crashes due to empty rbtree
> sched: Core-wide rq->lock
> sched/fair: Add a few assertions
> sched: Basic tracking of matching tasks
> sched: Add core wide task selection and scheduling.
> sched: Fix priority inversion of cookied task with sibling
> sched: Trivial forced-newidle balancer
> irq_work: Cleanup
> sched: CGroup tagging interface for core scheduling
>
> Vineeth Pillai (2):
> sched/fair: Fix forced idle sibling starvation corner case
> entry/kvm: Protect the kernel when entering from guest
>
> .../admin-guide/hw-vuln/core-scheduling.rst   |  330 +++++
> Documentation/admin-guide/hw-vuln/index.rst   |    1 +
> .../admin-guide/kernel-parameters.txt         |   25 +
> arch/x86/include/asm/thread_info.h            |    2 +
> arch/x86/kernel/cpu/bugs.c                    |   19 +
> arch/x86/kvm/x86.c                            |    2 +
> drivers/gpu/drm/i915/i915_request.c           |    4 +-
> include/linux/cpu.h                           |    1 +
> include/linux/entry-common.h                  |   30 +-
> include/linux/entry-kvm.h                     |   12 +
> include/linux/irq_work.h                      |   33 +-
> include/linux/irqflags.h                      |    4 +-
> include/linux/sched.h                         |   28 +-
> include/linux/sched/smt.h                     |    4 +
> include/uapi/linux/prctl.h                    |    3 +
> kernel/Kconfig.preempt                        |    5 +
> kernel/bpf/stackmap.c                         |    2 +-
> kernel/cpu.c                                  |   43 +
> kernel/entry/common.c                         |   28 +-
> kernel/entry/kvm.c                            |   33 +
> kernel/fork.c                                 |    1 +
> kernel/irq_work.c                             |   18 +-
> kernel/printk/printk.c                        |    6 +-
> kernel/rcu/tree.c                             |    3 +-
> kernel/sched/Makefile                         |    1 +
> kernel/sched/core.c                           | 1278 +++++++++++++++--
> kernel/sched/coretag.c                        |  819 +++++++++++
> kernel/sched/cpuacct.c                        |   12 +-
> kernel/sched/deadline.c                       |   38 +-
> kernel/sched/debug.c                          |   12 +-
> kernel/sched/fair.c                           |  313 +++-
> kernel/sched/idle.c                           |   24 +-
> kernel/sched/pelt.h                           |    2 +-
> kernel/sched/rt.c                             |   31 +-
> kernel/sched/sched.h                          |  315 +++-
> kernel/sched/stop_task.c                      |   14 +-
> kernel/sched/topology.c                       |    4 +-
> kernel/sys.c                                  |    3 +
> kernel/time/tick-sched.c                      |    6 +-
> kernel/trace/bpf_trace.c                      |    2 +-
> tools/include/uapi/linux/prctl.h              |    3 +
> tools/testing/selftests/sched/.gitignore      |    1 +
> tools/testing/selftests/sched/Makefile        |   14 +
> tools/testing/selftests/sched/config          |    1 +
> .../testing/selftests/sched/test_coresched.c  |  818 +++++++++++
> 45 files changed, 4033 insertions(+), 315 deletions(-)
> create mode 100644 Documentation/admin-guide/hw-vuln/core-scheduling.rst
> create mode 100644 kernel/sched/coretag.c
> create mode 100644 tools/testing/selftests/sched/.gitignore
> create mode 100644 tools/testing/selftests/sched/Makefile
> create mode 100644 tools/testing/selftests/sched/config
> create mode 100644 tools/testing/selftests/sched/test_coresched.c
>
> --
> 2.29.2.299.gdc1121823c-goog
>