Re: ehci-hcd affects hda speed

From: Rene Herman
Date: Tue Apr 15 2008 - 16:21:37 EST


On 15-04-08 21:56, Lev A. Melnikovsky wrote:

Sorry, I had virtually no time to answer earlier. If (hopefully) someone is still interested, here's my feedback

Interested yes, although being no longer in posession of the hardware it's a somewhat academic interest...

I have repeated experiments with P3B-F and VT6212L combination (to improve visibility the AsyncSchedSleepTime is set to 1us):

#0. Nothing is connected to USB, no ehci-hcd loaded
hda throughput 28+-1MB/s

#1. ehci-hcd loaded, still no USB peripherals
hda throughput 28+-1 MB/s

#2. Something (USB hub and FLASH drive tested) is attached
hda throughput 15+-1 MB/s

#3. All USB peripherals are removed
hda throughput 15+-1 MB/s

#4. ehci-hcd is rmmod'ed
hda throughput 28+-1MB/s

The oddest peculiarity for me is the hysteretic difference between #1 and #3 states. I mean experimental data (hda throughput) depends not on the state (hardware/loaded modules), but on the path we followed.

On the chip having inited itself at least. Yes, your results match what I experienced.

Interestingly enough, sampling registers (via /sys) often shows Async bit set of the status register in the state #3. It is always cleared in #1. The async file is empty in both states. I wonder, how many degrees of freedom does an empty schedule have? Does "empty" mean "has no incomplete requests" or "has no requests at all"? Just guessing...

Should leave this up to David, but as far as I'm aware "no at all".

RH> The sleep time wasn't the core problem, so I wonder of later VIA chips do
RH> still have the active async schedule problem...
I don't think this is purely VIA problem. I did not _try_ to install that VT6212L card into newer motherboard, but my _feeling_ is that we see an "incompatibility" between older PCI mobo chipsets and VIA USB controller.

I very much doubt that. Can't really imagine an off-silicon reason the chip would keep scanning the async schedule. I'm also now using a NEC controller card in that same machine and it also shows no problems.

Actually, taking into account superior PCI bandwidth of modern PCs (if compared with my old P3B-F motherboard) I am not sure we can perform a clean reliable test without PCI bus analyzer.

http://lkml.org/lkml/2005/5/30/259


-l


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