Subject: Re: [linux-audio-user] dipping toes in 2.6 waters
From: John Check (j4strngs_AT_bitless.net)
Date: Sun Aug 08 2004 - 01:50:29 EEST
On Saturday 07 August 2004 06:30 pm, Lee Revell wrote:
> On Sat, 2004-08-07 at 06:24, Florian Schmidt wrote:
> > do you know how, in the case of volountary preemption and threaded irq
> > handlers, the irq's used by X11 are handled? i removed the nvidia module
> > from my kernelvand rebooted to have it untainted, but of course the X11
> > nv module does neither report to /proc/interrupts nor /proc/irq. SInce
> > it is on another bus [agp] i suppose this is no problem but i always
> > wondered about the interplay of the kernel an X. It looks to me like an
> > area which might still have some surprises..
>
> I believe that video cards use interrupts for 3d engine completion - you
> tell the card to render such and such, rotate 30 degrees, zoom, and you
> get an interrupt when it's done and ready for the next command.
>
> There are certainly some surprises in this area. If 2D acceleration is
> enabled on my onboard Via CLE266 video, the 2D engine will cause
> interrupts from the PCI slot to be disabled for long periods. I am not
> sure yet if this a bug or a feature.
>
Tweaking the PCI latency timer values makes a big difference WRT the video
card hogging the buss. I know thats not what you're talking about per se, but
it's apropos WRT xruns/performance.
> I recommend disabling all hardware video acceleration when tuning a
> system for low latency (set Option "NoAccel" and commend out the "dri"
> line). This will prevent X from interacting directly with your hardware
> - it is complicated enough when only the kernel can access hardware.
> Then, once you get that working, re-enable 2D acceleration, then DRI/3D
> acceleration, if these do not cause problems. This will make it much
> easier to get the problematic video drivers fixed.
>
> Lee
Definitely a good strategy, but nobody is going to take a system with no
video acceleration seriously.
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