linux-kernel - Re: [RFC] maximum latency tracking infrastructure

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Message-ID: <44EEB425.8060707@yahoo.com.au>
Date:	Fri, 25 Aug 2006 18:26:13 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Arjan van de Ven <arjan@...ux.intel.com>
CC:	Jesse Barnes <jbarnes@...tuousgeek.org>,
	linux-kernel@...r.kernel.org, len.brown@...el.com,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [RFC] maximum latency tracking infrastructure

Arjan van de Ven wrote:
> Nick Piggin wrote:

>> Surely you would call set_acceptable_latency() *before* running such
>> operation that requires the given latency? And that 
>> set_acceptable_latency
>> would block the caller until all CPUs are set to wake within this 
>> latency.
>>
>> That would be the API semantics I would expect, anyway.
> 
> 
> but that means it blocks, and thus can't be used in irq context

Is that a problem? I guess it could be, but you don't want to
give a false sense of security either. Having an explicit _nosync
version may make that clear?

> 
> (the usage model I imagine happens most is a set_acceptable_latency() 
> which can block during device init,
> with either no or a very course limit, and a 
> modify_acceptable_latency(), which cannot block, from irq context or
> device open)

OK. You'd know more about that than I ;)

-- 
SUSE Labs, Novell Inc.
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