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

[Joel Fernandes <joel@joelfernandes.org>]

On Tue, Nov 24, 2020 at 6:48 AM Vincent Guittot
<vincent.guittot@linaro.org> wrote:
>
> 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

Apologies. I was just going by folks who were CC'd on previous series.
I am new to doing this series's postings.  Sorry if I missed you and
will run get_maintainers henceforth!

 - Joel


> > 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
> >