Re: false positive -ENOSPC in ohci-q

On Mon, Feb 26, 2007 at 08:07:59AM -0800, David Brownell wrote:
> On Monday 26 February 2007 7:11 am, Andrea Arcangeli wrote:
> > Hello,
> > 
> > until I applied the below patch I couldn't use the usb camera at the
> > same time of the usb modem (both usb1 devices). The camera returned
> > -ENOSPC. Now they both work fine at the same time (camera managed by
> > zoneminder and running all the time and the modem giving me the
> > internet link, both without any apparent problem).
> 
> NAK unless you can demonstrate a bug in the logic you disabled.

demonstrate a bug? I thought I already did. Things works perfectly
with that code disabled: zoneminder analyzes 8 frames per second while
my RTT latency to the other end of the modem is still 10msec and I get
zero errors and everything works flawlessy. With that broken code
compiled in, as soon as I connect to the internet the camera returns
-ENOSPC. What else could I ever need to do in order to demonstrate
that there is a bug in the logic that I disabled? I'm afraid I can't
provide a mathematical proof, cause I don't even understand what that
code is doing and what a worthless number 90% can ever be when things
may work perfectly at 95% load too (can you instead demonstrate that
90% is a correct max load instead of 95% or 100%?). Code like that
must be overoptimistic! it should catch over-exaggerate bandwidth
loads that are absolutely guaranteed to fail, it must not be
overstrict like it seems to be now, in turn generating false
positives.

Now if this is a hardware bug in the modem or the camera, I still
would need a runtime tweak to disable that heuristic that clearly
can choke in practice with real life usage (I can also imagine
hardware advertising a peak value, but if run in certain modes, like
with low res, generating lower max-values, so a runtime tweak to tell
the heuristic to go away still sounds useful even if this wouldn't be
a hardware issue and if the heuristic would be legitimate at only 90%).

> Looks more like your config is one that's disallowed.

I tried all possibile config and tweaks, so I doubt you can blame on me.

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