linux-kernel - Re: [RFC PATCH 5/5 single-thread-version] implement per-domain single-thread state machine call

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Message-ID: <20120410201512.GI2428@linux.vnet.ibm.com>
Date:	Tue, 10 Apr 2012 13:15:12 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	Lai Jiangshan <eag0628@...il.com>, linux-kernel@...r.kernel.org,
	mingo@...e.hu, dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org,
	niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com, darren@...art.com, fweisbec@...il.com,
	patches@...aro.org
Subject: Re: [RFC PATCH 5/5 single-thread-version] implement per-domain
 single-thread state machine call_srcu()

On Wed, Mar 14, 2012 at 03:47:06PM +0800, Lai Jiangshan wrote:
> On 03/13/2012 02:03 AM, Paul E. McKenney wrote:
> 
> >>
> >> In mb()-based srcu, synchronize_srcu() is very fast,
> >> synchronize_srcu_expedited() makes less sense than before.
> > 
> > I am worried about expedited callbacks getting backed up behind
> > non-expedited callbacks (especially given Peter's point about per-VMA
> > SRCU callbacks) and behind other workqueue uses.
> > 
> >> But when wait_srcu_gp() is move back here, I will use
> >> a bigger "trycount" for synchronize_srcu_expedited().
> >>
> >> And any problem for srcu_advance_batches()?
> > 
> > I prefer the use of "return" that you and Peter discussed later.
> > 
> > What sort of testing are you doing?
> 
> rcutorture in my box for several days on my daily used machine.

OK, good!

> What would you prefer for next round of patches, single-thread or per-cpu?
> I will send them soon.
> (per-cpu approach will be also "batches, in-sleepable, reuse rcu_head"....)
> 
> I prefer the single-thread approach until high-callback-rate-per-domain-era
> comes, but I don't know how long when it comes. Peter?

Well, the price for sticking with the single-thread approach is
a commitment on your part to create a high-callback-rate-per-domain
version at a moment's notice, should it be needed.

Can you commit to that?  If not, then the initial version needs to be
able to handle a high callback rate.

							Thanx, Paul

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