linux-kernel - Re: [RFC] Simple userspace interface for PCI drivers

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Date:	Thu, 31 Aug 2006 15:42:48 -0700
From:	Greg KH <greg@...ah.com>
To:	Manu Abraham <abraham.manu@...il.com>
Cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Andrew de Quincey <adq_dvb@...skialf.net>
Subject: Re: [RFC] Simple userspace interface for PCI drivers

On Thu, Aug 31, 2006 at 05:24:30PM +0400, Manu Abraham wrote:
> Usually in the typical application we have (where latency is an issue),
> most probably many of the people have a saturated PCI bus. In most
> cases, the IPTV guys have such a scenario. Say > 6 or 7 DVB adapters and
> the latency goes very high.

Sure, when you are pushing your hardware to the maximum, you should
expect issues like this.  I agree we should do as best as we can for
things like this, but when you over-subscribe your PCI bus by doing
something like this, I really recommend just buying some hardware that
will work better for you (separate PCI busses, etc.  The hardware is out
there to do this properly.)

> What i have seen is that when the bus gets saturated, the CPU usage
> shoots of rather abnormally.

As is to be expected.

> When the latency goes higher, the resultant stream is useless and
> packets needs to be dropped, eventually that results in Transport
> Stream discontinuities.

Sure, that's understandable.

> Currently we already have a latency issue, based on the loud cries
> from some people.

Trying to do things the hardware is not ment to do, should not result in
cries from users :)

thanks,

greg k-h
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