linux-kernel - Re: [GIT PULL rcu/urgent] Auto-expedite initial SRCU grace periods

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Date:   Thu, 27 Apr 2017 08:11:40 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:     linux-kernel@...r.kernel.org, efault@....de,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [GIT PULL rcu/urgent] Auto-expedite initial SRCU grace periods


* Paul E. McKenney <paulmck@...ux.vnet.ibm.com> wrote:

> Hello, Ingo,
> 
> This series greatly reduces the performance degradation of Tree SRCU
> on a CPU-hotplug stress test.  The effect was not subtle:  Mike Galbraith
> measured Classic SRCU at 55 seconds and Tree SRCU at more than 16 -minutes-
> for this test.  Mike collected ftrace data that showed that Classic SRCU
> was auto-expediting invocations of synchronize_srcu() that found SRCU
> completely idle.  This series therefore adds this auto-expedite capability
> to Tree SRCU, bringing the performance shortfall to less than ten seconds,
> which is a great improvement over the initial shortfall of 15 minutes.
> 
> I will continue tuning, but this improvement seemed worth a pull request,
> in order to get the base solution some more test time in -tip.  Note that
> two of the commits are not strictly necessary, but they are reasonably
> simple, they conflict with the three main commits, and the risk of
> disentangling them seemed to greatly exceed the risk of pushing them in.
> Of course, if you believe that they really should be delayed, please let
> me know and I can disentangle them.  They are: (1) c7e88067c1ae ("srcu:
> Exact tracking of srcu_data structures containing callbacks") and
> (2) 7f6733c3c648 ("srcu: Make rcutorture writer stalls print SRCU GP
> state").
> 
> These commits are available in the git repository at:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git rcu/urgent
> 
> for you to fetch changes up to 22607d66bbc3e81140d3bcf08894f4378eb36428:
> 
>   srcu: Specify auto-expedite holdoff time (2017-04-26 16:32:17 -0700)
> 
> ----------------------------------------------------------------
> Paul E. McKenney (5):
>       srcu: Exact tracking of srcu_data structures containing callbacks
>       srcu: Make rcutorture writer stalls print SRCU GP state
>       srcu: Expedited grace periods with reduced memory contention
>       srcu: Expedite first synchronize_srcu() when idle
>       srcu: Specify auto-expedite holdoff time
> 
>  Documentation/admin-guide/kernel-parameters.txt |   8 +
>  include/linux/srcuclassic.h                     |  14 ++
>  include/linux/srcutiny.h                        |  12 ++
>  include/linux/srcutree.h                        |  13 +-
>  kernel/rcu/rcutorture.c                         |   8 +-
>  kernel/rcu/srcutree.c                           | 242 ++++++++++++++++++++----
>  kernel/rcu/tree.c                               |  12 +-
>  7 files changed, 255 insertions(+), 54 deletions(-)

Pulled, thanks a lot Paul!

	Ingo