Re: [PATCH RFC 00/16] A new RCU implementation based on a fast consensus protocol

From: Paul E. McKenney
Date: Sat Jan 27 2018 - 18:42:45 EST

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On Fri, Jan 26, 2018 at 11:57:44PM -0800, Paul E. McKenney wrote:
> On Sat, Jan 27, 2018 at 07:22:27AM +0000, Lihao Liang wrote:
> > On Thu, Jan 25, 2018 at 5:53 AM, Paul E. McKenney
> > <paulmck@xxxxxxxxxxxxxxxxxx> wrote:
> > > On Tue, Jan 23, 2018 at 03:59:25PM +0800, lianglihao@xxxxxxxxxx wrote:
> > >> From: Lihao Liang <lianglihao@xxxxxxxxxx>
> > >>
> > >> Dear Paul,
> > >>
> > >> This patch set implements a preemptive version of RCU (PRCU) based on the following paper:
> > >>
> > >> Fast Consensus Using Bounded Staleness for Scalable Read-mostly Synchronization.
> > >> Haibo Chen, Heng Zhang, Ran Liu, Binyu Zang, and Haibing Guan.
> > >> IEEE Transactions on Parallel and Distributed Systems (TPDS), 2016.
> > >> https://dl.acm.org/citation.cfm?id=3024114.3024143
> > >>
> > >> We have also added preliminary callback-handling support. Thus, the current version
> > >> provides APIs prcu_read_lock(), prcu_read_unlock(), synchronize_prcu(), call_prcu(),
> > >> and prcu_barrier().
> > >>
> > >> This is an experimental patch, so it would be good to have some feedback.
> > >>
> > >> Known shortcoming is that the grace-period version is incremented in synchronize_prcu().
> > >> If call_prcu() or prcu_barrier() is called but there is no synchronized_prcu() invoked,
> > >> callbacks cannot be invoked. Later version should address this issue, e.g. adding a
> > >> grace-period expedition mechanism. Others include to use a a hierarchical structure,
> > >> taking into account the NUMA topology, to send IPI in synchronize_prcu().
> > >>
> > >> We have tested the implementation using rcutorture on both an x86 and ARM64 machine.
> > >> PRCU passed 1h and 3h tests on all the newly added config files except PRCU07 reported BUG
> > >> in a 1h run.
> > >>
> > >> [ 1593.604201] ---[ end trace b3bae911bec86152 ]---
> > >> [ 1594.629450] prcu-torture:torture_onoff task: offlining 14
> > >> [ 1594.755553] smpboot: CPU 14 is now offline
> > >> [ 1594.757732] prcu-torture:torture_onoff task: offlined 14
> > >> [ 1597.765149] prcu-torture:torture_onoff task: onlining 11
> > >> [ 1597.766795] smpboot: Booting Node 0 Processor 11 APIC 0xb
> > >> [ 1597.804102] prcu-torture:torture_onoff task: onlined 11
> > >> [ 1599.365098] prcu-torture: rtc: ffffffffb0277b90 ver: 66358 tfle: 0 rta: 66358 rtaf: 0
> > >> rtf: 66349 rtmbe: 0 rtbe: 1 rtbke: 0 rtbre: 0 rtbf: 0 rtb: 0 nt: 2233418
> > >> onoff: 191/191:199/199 34,199:59,5102 10403:0 (HZ=1000) barrier: 188/189:1 cbflood: 225
> > >> [ 1599.367946] prcu-torture: !!!
> > >> [ 1599.367966] ------------[ cut here ]------------
> > >
> > > The "rtbe: 1" indicates that your implementation of prcu_barrier()
> > > failed to wait for all preceding call_prcu() callbacks to be invoked.

And my guess is that the "rtbe: 1" is happening because you aren't doing
anything with CPU hotplug. The way this could happen is as follows:

1. rcutorture does call_prcu() with a test callback on CPU 5.

2. CPU 5 goes offline, but its callbacks stay there.

3. rcutorture does prcu_barrier(), which queues a callback on each
sufficiently online CPU. No callback is enqueued on CPU 5.

4. The enqueued callbacks are all invoked, so prcu_barrier()
returns.

5. rcutorture complains because the test callback stranded on CPU 5
never did get invoked.

A slightly different sequence of events could strand one of prcu_barrier()'s
callbacks on an offline CPU, in which case prcu_barrier() would hang until
that CPU came back online. There are probably other failure scenarios, but
those two should do for now. ;-)

Thanx, Paul

> > > Does the immediately following "Reader Pipe:" list have any but the
> > > first two numbers non-zero?
> >
> > Yes.
>
> If the third or subsequent numbers are non-zero, that would indicate
> too-short grace periods. This would be a critical bug in PRCU.
>
> > >> We have also compared PRCU with TREE RCU using rcuperf with gp_exp set to true, that is
> > >> synchronize_rcu_expedited was tested.
> > >>
> > >> The rcuperf results are as follows (average grace-period duration in ms of ten 10min runs):
> > >>
> > >> 16*Intel Xeon CPU@xxxxxx, 16GB memory, Ubuntu Linux 3.13.0-47-generic
> > >>
> > >> CPUs 2 4 8 12 15 16
> > >> PRCU 0.14 1.07 4.15 8.02 10.79 15.16
> > >> TREE 49.30 104.75 277.55 390.82 620.82 1381.54
> > >>
> > >> 64*Cortex-A72 CPU@xxxxxx, 130GB memory, Ubuntu Linux 4.10.0-21.23-generic
> > >>
> > >> CPUs 2 4 8 16 32 48 63 64
> > >> PRCU 0.23 19.69 38.28 63.21 95.41 167.18 252.01 1841.44
> > >> TREE 416.73 901.89 1060.86 743.00 920.66 1325.21 1646.20 23806.27
> > >
> > > Well, at the very least, this is a bug report on either expedited RCU
> > > grace-period latency or on rcuperf's measurements, and thank you for that.
> > > I will look into this. In the meantime, could you please let me know
> > > exactly how you invoked rcuperf?
> >
> > We used the following command to invoke rcuperf:
> >
> > sudo ./kvm.sh --torture rcuperf --duration 10 --configs 10*TREE
> >
> > The actual script run-rcuperf.sh to run the experiments can be found
> > in the following email of this patch series:
> >
> > [PATCH RFC 15/16] rcutorture: Add scripts to run experiments
> >
> > Please let us know how it goes.
>
> Will do!
>
> As I said before, at the very least you have identified a performance bug
> in RCU expedited grace periods.
>
> Thanx, Paul
>
> > Many thanks,
> > Lihao.
> >
> > > I have a few comments on some of your patches based on a quick scan
> > > through them.
> > >
> > > Thanx, Paul
> > >
> > >> Best wishes,
> > >> Lihao.
> > >>
> > >>
> > >> Lihao Liang (15):
> > >> rcutorture: Add PRCU rcu_torture_ops
> > >> rcutorture: Add PRCU test config files
> > >> rcuperf: Add PRCU rcu_perf_ops
> > >> rcuperf: Add PRCU test config files
> > >> rcuperf: Set gp_exp to true for tests to run
> > >> prcu: Implement call_prcu() API
> > >> prcu: Implement PRCU callback processing
> > >> prcu: Implement prcu_barrier() API
> > >> rcutorture: Test call_prcu() and prcu_barrier()
> > >> rcutorture: Add basic ARM64 support to run scripts
> > >> prcu: Add PRCU Kconfig parameter
> > >> prcu: Comment source code
> > >> rcuperf: Add config files with various CONFIG_NR_CPUS
> > >> rcutorture: Add scripts to run experiments
> > >> Add GPLv2 license
> > >>
> > >> Heng Zhang (1):
> > >> prcu: Add PRCU implementation
> > >>
> > >> include/linux/interrupt.h | 3 +
> > >> include/linux/prcu.h | 122 +++++
> > >> include/linux/rcupdate.h | 1 +
> > >> init/Kconfig | 7 +
> > >> init/main.c | 2 +
> > >> kernel/rcu/Makefile | 1 +
> > >> kernel/rcu/prcu.c | 497 +++++++++++++++++++++
> > >> kernel/rcu/rcuperf.c | 33 +-
> > >> kernel/rcu/rcutorture.c | 40 +-
> > >> kernel/rcu/tree.c | 1 +
> > >> kernel/sched/core.c | 2 +
> > >> kernel/time/timer.c | 2 +
> > >> kvm.sh | 452 +++++++++++++++++++
> > >> run-rcuperf.sh | 26 ++
> > >> .../testing/selftests/rcutorture/bin/functions.sh | 17 +-
> > >> .../selftests/rcutorture/configs/rcu/CFLIST | 5 +
> > >> .../selftests/rcutorture/configs/rcu/PRCU02 | 27 ++
> > >> .../selftests/rcutorture/configs/rcu/PRCU02.boot | 1 +
> > >> .../selftests/rcutorture/configs/rcu/PRCU03 | 23 +
> > >> .../selftests/rcutorture/configs/rcu/PRCU03.boot | 2 +
> > >> .../selftests/rcutorture/configs/rcu/PRCU06 | 26 ++
> > >> .../selftests/rcutorture/configs/rcu/PRCU06.boot | 5 +
> > >> .../selftests/rcutorture/configs/rcu/PRCU07 | 25 ++
> > >> .../selftests/rcutorture/configs/rcu/PRCU07.boot | 2 +
> > >> .../selftests/rcutorture/configs/rcu/PRCU09 | 19 +
> > >> .../selftests/rcutorture/configs/rcu/PRCU09.boot | 1 +
> > >> .../selftests/rcutorture/configs/rcuperf/CFLIST | 1 +
> > >> .../selftests/rcutorture/configs/rcuperf/PRCU | 20 +
> > >> .../selftests/rcutorture/configs/rcuperf/PRCU-12 | 21 +
> > >> .../rcutorture/configs/rcuperf/PRCU-12.boot | 1 +
> > >> .../selftests/rcutorture/configs/rcuperf/PRCU-14 | 21 +
> > >> .../rcutorture/configs/rcuperf/PRCU-14.boot | 1 +
> > >> .../selftests/rcutorture/configs/rcuperf/PRCU-15 | 21 +
> > >> .../rcutorture/configs/rcuperf/PRCU-15.boot | 1 +
> > >> .../selftests/rcutorture/configs/rcuperf/PRCU-16 | 21 +
> > >> .../rcutorture/configs/rcuperf/PRCU-16.boot | 1 +
> > >> .../selftests/rcutorture/configs/rcuperf/PRCU-2 | 21 +
> > >> .../rcutorture/configs/rcuperf/PRCU-2.boot | 1 +
> > >> .../selftests/rcutorture/configs/rcuperf/PRCU-32 | 21 +
> > >> .../rcutorture/configs/rcuperf/PRCU-32.boot | 1 +
> > >> .../selftests/rcutorture/configs/rcuperf/PRCU-4 | 21 +
> > >> .../rcutorture/configs/rcuperf/PRCU-4.boot | 1 +
> > >> .../selftests/rcutorture/configs/rcuperf/PRCU-48 | 21 +
> > >> .../rcutorture/configs/rcuperf/PRCU-48.boot | 1 +
> > >> .../selftests/rcutorture/configs/rcuperf/PRCU-56 | 21 +
> > >> .../rcutorture/configs/rcuperf/PRCU-56.boot | 1 +
> > >> .../selftests/rcutorture/configs/rcuperf/PRCU-60 | 21 +
> > >> .../rcutorture/configs/rcuperf/PRCU-60.boot | 1 +
> > >> .../selftests/rcutorture/configs/rcuperf/PRCU-62 | 21 +
> > >> .../rcutorture/configs/rcuperf/PRCU-62.boot | 1 +
> > >> .../selftests/rcutorture/configs/rcuperf/PRCU-64 | 21 +
> > >> .../rcutorture/configs/rcuperf/PRCU-64.boot | 1 +
> > >> .../selftests/rcutorture/configs/rcuperf/PRCU-8 | 21 +
> > >> .../rcutorture/configs/rcuperf/PRCU-8.boot | 1 +
> > >> .../selftests/rcutorture/configs/rcuperf/PRCU.boot | 1 +
> > >> .../selftests/rcutorture/configs/rcuperf/TREE-12 | 21 +
> > >> .../selftests/rcutorture/configs/rcuperf/TREE-14 | 21 +
> > >> .../selftests/rcutorture/configs/rcuperf/TREE-15 | 21 +
> > >> .../selftests/rcutorture/configs/rcuperf/TREE-16 | 21 +
> > >> .../selftests/rcutorture/configs/rcuperf/TREE-2 | 21 +
> > >> .../selftests/rcutorture/configs/rcuperf/TREE-32 | 21 +
> > >> .../selftests/rcutorture/configs/rcuperf/TREE-4 | 21 +
> > >> .../selftests/rcutorture/configs/rcuperf/TREE-48 | 21 +
> > >> .../selftests/rcutorture/configs/rcuperf/TREE-56 | 21 +
> > >> .../selftests/rcutorture/configs/rcuperf/TREE-60 | 21 +
> > >> .../selftests/rcutorture/configs/rcuperf/TREE-62 | 21 +
> > >> .../selftests/rcutorture/configs/rcuperf/TREE-64 | 21 +
> > >> .../selftests/rcutorture/configs/rcuperf/TREE-8 | 21 +
> > >> 68 files changed, 1918 insertions(+), 5 deletions(-)
> > >> create mode 100644 include/linux/prcu.h
> > >> create mode 100644 kernel/rcu/prcu.c
> > >> create mode 100755 kvm.sh
> > >> create mode 100755 run-rcuperf.sh
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcu/PRCU02
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcu/PRCU02.boot
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcu/PRCU03
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcu/PRCU03.boot
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcu/PRCU06
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcu/PRCU06.boot
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcu/PRCU07
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcu/PRCU07.boot
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcu/PRCU09
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcu/PRCU09.boot
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-12
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-12.boot
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-14
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-14.boot
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-15
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-15.boot
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-16
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-16.boot
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-2
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-2.boot
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-32
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-32.boot
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-4
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-4.boot
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-48
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-48.boot
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-56
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-56.boot
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-60
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-60.boot
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-62
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-62.boot
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-64
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-64.boot
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-8
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU-8.boot
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/PRCU.boot
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/TREE-12
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/TREE-14
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/TREE-15
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/TREE-16
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/TREE-2
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/TREE-32
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/TREE-4
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/TREE-48
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/TREE-56
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/TREE-60
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/TREE-62
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/TREE-64
> > >> create mode 100644 tools/testing/selftests/rcutorture/configs/rcuperf/TREE-8
> > >>
> > >> --
> > >> 2.14.1.729.g59c0ea183
> > >>
> > >
> >

Next message: Paul E. McKenney: "Re: [PATCH RFC 00/16] A new RCU implementation based on a fast consensus protocol"
Previous message: Michal SuchÃnek: "Re: [PATCH resend 0/6] Fix cdrom autoclose"
In reply to: Paul E. McKenney: "Re: [PATCH RFC 00/16] A new RCU implementation based on a fast consensus protocol"
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