linux-kernel - Re: [PATCH tip/core/rcu 0/21] Contention reduction for v4.18

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Message-Id: <20180514160907.GX26088@linux.vnet.ibm.com>
Date:   Mon, 14 May 2018 09:09:07 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Nicholas Piggin <nicholas.piggin@...il.com>
Cc:     linux-kernel@...r.kernel.org, mingo@...nel.org,
        jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com, joel.opensrc@...il.com,
        torvalds@...ux-foundation.org, npiggin@...il.com
Subject: Re: [PATCH tip/core/rcu 0/21] Contention reduction for v4.18

On Mon, May 14, 2018 at 04:42:33PM +1000, Nicholas Piggin wrote:
> On Sun, 22 Apr 2018 20:02:58 -0700
> "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:
> 
> > Hello!
> > 
> > This series reduces lock contention on the root rcu_node structure,
> > and is also the first precursor to TBD changes to consolidate the
> > three RCU flavors (RCU-bh, RCU-preempt, and RCU-sched) into one.
> 
> Hi Paul,
> 
> I've been running your rcu/dev branch and haven't noticed any problems
> yet. The irqsoff latency improvement is a little hard to measure
> because the scheduler, but I've tried turning balancing parameters
> right down and I'm yet to see any sign of RCU in traces (down to about
> 100us on a 176 CPU machine), so that's great.

Good to hear!!!

> (Not that RCU was ever the worst contributor to latency as I said, just
> that I noticed those couple of traces where it showed up.)
> 
> Thanks very much for the fast response, sorry I've taken a while to
> test.

Would you be willing to give me a Tested-by on that series of patches?

							Thanx, Paul