Date: Fri, 20 Feb 2015 10:39:27 -0800
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Arjan van de Ven <arjan@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>, linux-kernel@vger.kernel.org,
        mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com,
        akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
        josh@joshtriplett.org, tglx@linutronix.de, rostedt@goodmis.org,
        dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com,
        fweisbec@gmail.com, oleg@redhat.com, bobby.prani@gmail.com
Subject: Re: [PATCH tip/core/rcu 0/4] Programmatic nestable expedited grace
 periods
Message-ID: <20150220183927.GP5745@linux.vnet.ibm.com>
Reply-To: paulmck@linux.vnet.ibm.com
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 <20150220163737.GL5745@linux.vnet.ibm.com>
 <20150220165409.GU5029@twins.programming.kicks-ass.net>
 <20150220171442.GM5745@linux.vnet.ibm.com>
 <54E76FB7.4060005@linux.intel.com>
 <20150220182745.GN5745@linux.vnet.ibm.com>
 <54E77D0E.6060000@linux.intel.com>
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On Fri, Feb 20, 2015 at 10:29:34AM -0800, Arjan van de Ven wrote:
> On 2/20/2015 10:27 AM, Paul E. McKenney wrote:
> >On Fri, Feb 20, 2015 at 09:32:39AM -0800, Arjan van de Ven wrote:
> >>>>>>Does it really make a machine boot much faster? Why are people using
> >>>>>>synchronous gp primitives if they care about speed? Should we not fix
> >>>>>>that instead?
> >>>>>
> >>>>>The report I heard was that it provided 10-15% faster boot times.
> >>>>
> >>>>That's not insignificant; got more details? I think we should really
> >>>>look at why people are using the sync primitives.
> >>>
> >>>I must defer to the people who took the exact measurements.
> >>>
> >>>But yes, once I have that info, I should add it to the commit log.
> >>
> >>so the two most obvious cases are
> >>
> >>Registering sysrq keys ... even when the old key code had no handler
> >>(have a patch pending for this)
> >>
> >>registering idle handlers
> >>(this is more tricky, it's very obvious abuse but the fix is less clear)
> >>
> >>there's a few others as well that I'm chasing down...
> >>.. but the flip side, prior to running ring 3 code, why NOT do fast expedites?
> >
> >It would be good to have before-and-after measurements of actual
> >boot time.  Are these numbers available?
> 
> I'll make you pretty graphs when I get home from collab summit, which
> should be later today

Very good, looking forward to seeing them.  ;-)

							Thanx, Paul

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