This is a message I posted to linux-kernel today. There is a problem
with the via DRI driver causing interrupts to be disabled for long
periods. The board is an EPIA ME-6000. I am using Debian unstable.
On Wed, 2004-07-14 at 18:19, Lee Revell wrote:
> It seems that interrupts are being disabled for long periods,
> resulting in the soundcard interrupt being lost. I hacked the
> ALSA emu10k1 driver to keep track in the interrupt handler of
> the number of CPU cycles elapsed since the last time it ran.
> I am using a period that corresponds to 666 microseconds between
> interrupts, or ~400000 cycles on my 600Mhz CPU. As you can see the
> average jitter is *extremely* low - 50-400 CPU cycles of per interrupt.
> I hardcoded it to printk if the jitter is more than 15000 (only happens
> every 5-10 seconds), and error if it's really big. As you can see,
> something is disabling interrupts for a long time. This is a completely
> different issue from an XRUN, improving the scheduler latency will not
> solve this.
The problem is with the video driver (Via CastleRock integrated,
AGP4x). By dragging a window in X more quickly than the machine can
keep up with, I can reliably cause interrupts to be completely disabled
for tens or hundreds of milliseconds.
There was an issue several years ago where Matrox figured out they could
get slightly better benchmark scores by not checking whether a FIFO on
the video card was full before writing to it, which would cause the PCI
bus to completely freeze until the FIFO had drained. Lots of vendors
followed suit until one of the audio software vendors figred it out and
called them on it, at which point they fixed their drivers. The effects
(massive audio drouputs) and the steps to reproduce (drag a window
around the screen) were identical.
Here is the lspci output:
0000:01:00.0 VGA compatible controller: VIA Technologies, Inc. VT8623
[Apollo CLE266] integrated CastleRock graphics (rev 03) (prog-if 00
[VGA])
Subsystem: VIA Technologies, Inc. VT8623 [Apollo CLE266]
integrated CastleRock graphics
Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop-
ParErr- Stepping- SERR- FastB2B-
Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=medium >TAbort-
<TAbort- <MAbort- >SERR- <PERR-
Latency: 32 (500ns min)
Interrupt: pin A routed to IRQ 11
Region 0: Memory at e4000000 (32-bit, prefetchable) [size=64M]
Region 1: Memory at e8000000 (32-bit, non-prefetchable)
[size=16M]
Capabilities: [60] Power Management version 2
Flags: PMEClk- DSI+ D1+ D2+ AuxCurrent=0mA
PME(D0-,D1-,D2-,D3hot-,D3cold-)
Status: D0 PME-Enable- DSel=0 DScale=0 PME-
Capabilities: [70] AGP version 2.0
Status: RQ=32 Iso- ArqSz=0 Cal=0 SBA+ ITACoh- GART64-
HTrans- 64bit- FW- AGP3- Rate=x1,x2,x4
Command: RQ=1 ArqSz=0 Cal=0 SBA- AGP- GART64- 64bit- FW-
Rate=<none>
Lee
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