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Message-ID: <alpine.LFD.0.999.0708202316430.30176@woody.linux-foundation.org>
Date: Mon, 20 Aug 2007 23:25:13 -0700 (PDT)
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Arjan van de Ven <arjan@...radead.org>
cc: David Brownell <david-b@...bell.net>,
Michal Piotrowski <michal.k.k.piotrowski@...il.com>,
linux-usb-devel@...ts.sourceforge.net, Greg KH <gregkh@...e.de>,
LKML <linux-kernel@...r.kernel.org>,
"Stuart_Hayes@...l.com" <Stuart_Hayes@...l.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Daniel Exner <dex@...gonslave.de>
Subject: Re: [linux-usb-devel] [4/4] 2.6.23-rc3: known regressions
On Mon, 20 Aug 2007, Arjan van de Ven wrote:
> >
> > So it might be much better if we instead re-introduced that kind of "DMA
> > latency requirement", and letting different subsystems react to that as
> > they may.
>
> wait.... we HAVE that infrastructure .. see kernel/latency.c ...
Heh. Just shows how wellknown that interface is - it seems like it's only
used by the ipw2100 driver and "pcm_native".
But yes, that looks like the right thing.
> and the C-state code will honor it. CPUFREQ doesn't honor it yet but
> that's easy to add.. (this assumes the ACPI BIOS informs us correctly
> about the cpu behavior, but that's the best we can do obviously unless
> you want a table inside the kernel keyed off vendor/model/stepping)
Do we actually have the latency information for these things? Especially
since I assume a number of people use the specialized direct-hw-access
cpufreq drivers..
I realize that we *have* "transition_latency" at the cpufreq layer, and it
is supposed to be in ns, but I wonder how likely it is to bear any
relationship to reality, considering that I don't think it's really used
for anything.. (yeah, it affects the heuristics, but I don't think it has
any _hard_ meaning, so I'd worry that it's not necessarily something that
people have tried to make accurate).
But I dunno.
Linus
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