linux-kernel - Re: [PATCH]PCIE ASPM support

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Message-ID: <7566.1200475868@turing-police.cc.vt.edu>
Date:	Wed, 16 Jan 2008 04:31:08 -0500
From:	Valdis.Kletnieks@...edu
To:	Shaohua Li <shaohua.li@...el.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	linux-pci <linux-pci@...ey.karlin.mff.cuni.cz>,
	Greg KH <greg@...ah.com>,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	"Kok, Auke" <auke-jan.h.kok@...el.com>
Subject: Re: [PATCH]PCIE ASPM support - takes 2

On Wed, 16 Jan 2008 13:26:14 +0800, Shaohua Li said:
> On Tue, 2008-01-15 at 22:56 -0500, Valdis.Kletnieks@...edu wrote:
> > Do you have any numbers on what the added latency is for powersave mode, and
> > a rough idea of how quickly chipsets will drop to low-power? It may affect
> > usability a lot if it's "adds 10ms latency after 100ms idle" or "adds 100ms
> > latency after 5 seconds idle" or some other pattern...
> >
> > (The chipset in my laptop claims to be an 82801G with 4 PCI-Express ports on
> > it - I'm trying to get a rough idea what usage I'd get out of that feature..)
> No, I thought to get the latency impact with ASPM enabled, but haven't
> found a way to measure it. This is why the default setting of ASPM
> currently is using BIOS setting.

It's OK - I spent some time staring at the output of 'lspci -t' on this laptop,
and convinced myself that the numbers won't matter that much - of the 4 PCIE
ports alledged to be there, 2 aren't connected to anything, and the other 2 are
network (a tg3 and an intel 3945) - and those two are both either (depending
where I am) "essentially idle and will almost certainly sleep" or "busy enough
they likely won't sleep no matter *what* the numbers are".

(That's assuming the chipset in question even *does* ASPM - but it wouldn't be
the first time I've tested stuff just to make sure it didn't enable an impossible
hardware option.. ;)

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