linux-kernel - Re: [PATCH RFC tip/core/rcu 0/5] Expedited grace periods encouraging normal ones

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Message-ID: <20150702021838.GA3717@linux.vnet.ibm.com>
Date:	Wed, 1 Jul 2015 19:18:38 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Mike Galbraith <umgwanakikbuti@...il.com>
Cc:	josh@...htriplett.org, Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, mingo@...nel.org,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	tglx@...utronix.de, rostedt@...dmis.org, dhowells@...hat.com,
	edumazet@...gle.com, dvhart@...ux.intel.com, fweisbec@...il.com,
	oleg@...hat.com, bobby.prani@...il.com
Subject: Re: [PATCH RFC tip/core/rcu 0/5] Expedited grace periods encouraging
 normal ones

On Thu, Jul 02, 2015 at 03:59:55AM +0200, Mike Galbraith wrote:
> On Wed, 2015-07-01 at 18:34 -0700, josh@...htriplett.org wrote:
> > On Thu, Jul 02, 2015 at 03:11:24AM +0200, Mike Galbraith wrote:
> > > On Wed, 2015-07-01 at 09:17 -0700, Paul E. McKenney wrote:
> > > > On Wed, Jul 01, 2015 at 04:17:10PM +0200, Peter Zijlstra wrote:
> > > > > On Wed, Jul 01, 2015 at 07:00:31AM -0700, Paul E. McKenney wrote:
> > > > > 
> > > > > > That is a bit extreme, Peter.
> > > > > 
> > > > > Of course; but I'm really not seeing people taking due care with them
> > > > 
> > > > ;-)
> > > > 
> > > > > > Are a huge pile of them coming in this merge window or something?
> > > > > > What raised your concerns on this issue?
> > > > > 
> > > > > This is complete horse manure (breaking the nvidiot binary blob is a
> > > > > good thing):
> > > > > 
> > > > > 74b51ee152b6 ("ACPI / osl: speedup grace period in acpi_os_map_cleanup")
> > > > 
> > > > Really???
> > > > 
> > > > I am not concerned about this one.  After all, one of the first things
> > > > that people do for OS-jitter-sensitive workloads is to get rid of
> > > > binary blobs.
> > > 
> > > I know two users who have no choice but to use the nvidia driver with
> > > their realtime applications, as nouveau is not up to the task.
> > 
> > Sounds like they have a relatively loose definition of "realtime", then.
> 
> It would be better it they broke their beasts up into a bunch of small
> synchronized boxen, but they use big boxen here and now, with realtime
> rendering being a non-disposable portion of the load.

Does their normal workload trigger the condition that results in the
expedited grace period?  If so, do they use NO_HZ_FULL?  (I am guessing
"no".)  If not, is the resulting double-context-switch on their worker
CPUs a real problem for them?  (I am guessing "no" given that they have
not complained, at least not that I know of.)

							Thanx, Paul

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