Message-ID: <54E77D0E.6060000@linux.intel.com>
Date: Fri, 20 Feb 2015 10:29:34 -0800
From: Arjan van de Ven <arjan@linux.intel.com>
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CC: Peter Zijlstra <peterz@infradead.org>, linux-kernel@vger.kernel.org,
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Subject: Re: [PATCH tip/core/rcu 0/4] Programmatic nestable expedited grace
 periods
References: <20150220050850.GA32639@linux.vnet.ibm.com> <20150220091107.GN21418@twins.programming.kicks-ass.net> <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>
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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

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