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Date: Tue, 24 Nov 2020 12:48:46 +0100
From: Vincent Guittot <vincent.guittot@...aro.org>
To: "Joel Fernandes (Google)" <joel@...lfernandes.org>
Cc: Nishanth Aravamudan <naravamudan@...italocean.com>,
Julien Desfossez <jdesfossez@...italocean.com>,
Peter Zijlstra <peterz@...radead.org>,
Tim Chen <tim.c.chen@...ux.intel.com>,
Vineeth Pillai <viremana@...ux.microsoft.com>,
Aaron Lu <aaron.lwe@...il.com>,
Aubrey Li <aubrey.intel@...il.com>,
Thomas Gleixner <tglx@...utronix.de>,
linux-kernel <linux-kernel@...r.kernel.org>,
Ingo Molnar <mingo@...nel.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Frederic Weisbecker <fweisbec@...il.com>,
Kees Cook <keescook@...omium.org>, kerrnel@...gle.com,
Phil Auld <pauld@...hat.com>,
Valentin Schneider <valentin.schneider@....com>,
Mel Gorman <mgorman@...hsingularity.net>,
Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
Paolo Bonzini <pbonzini@...hat.com>, vineeth@...byteword.org,
Chen Yu <yu.c.chen@...el.com>,
Christian Brauner <christian.brauner@...ntu.com>,
Agata Gruza <agata.gruza@...el.com>,
Antonio Gomez Iglesias <antonio.gomez.iglesias@...el.com>,
graf@...zon.com, konrad.wilk@...cle.com, dfaggioli@...e.com,
Paul Turner <pjt@...gle.com>,
Steven Rostedt <rostedt@...dmis.org>, derkling@...gle.com,
Jiang Biao <benbjiang@...cent.com>,
Alexandre Chartre <alexandre.chartre@...cle.com>,
James Bottomley <James.Bottomley@...senpartnership.com>,
OWeisse@...ch.edu, Dhaval Giani <dhaval.giani@...cle.com>,
Junaid Shahid <junaids@...gle.com>, jsbarnes@...gle.com,
"Hyser,Chris" <chris.hyser@...cle.com>,
Ben Segall <bsegall@...gle.com>, Josh Don <joshdon@...gle.com>,
Hao Luo <haoluo@...gle.com>,
Tom Lendacky <thomas.lendacky@....com>,
Aubrey Li <aubrey.li@...ux.intel.com>,
"Paul E. McKenney" <paulmck@...nel.org>,
Tim Chen <tim.c.chen@...el.com>
Subject: Re: [PATCH -tip 00/32] Core scheduling (v9)
Hi Joel,
On Wed, 18 Nov 2020 at 00:20, Joel Fernandes (Google)
<joel@...lfernandes.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
>
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