RPI3 swap experiments

[bob prohaska]

On Fri, Jun 29, 2018 at 05:37:50PM -0600, Warner Losh wrote:
> 
> 
> The drive is broken somewhere at or below the SIM. Reasonable write
> requests from CAM's periph da are being rejected. This tells me there's a
> problem. In this case, the SIM is umass which additionally has the USB
> stack under it. If I had to wager, I'd wager more on the USB driver being
> wonky than umass. Something is happening, and the SIM is returning an error
> to the periph. You're next step in tracking this down would be to see why
> by instrumenting umass' xpt_done calls that complete the CCBs that are
> queued by the sim's action routine.
> 
By "instrumenting" I don't think you mean wires and 'scopes......dtrace, maybe?
It's clear this is over my head, but I'll ask a further indulgence.

Using figure 2 at
https://people.freebsd.org/~imp/bsdcan2015/iosched-v3.pdf
or a better one if it exists, where on the diagram would the problem likely be?
It's pretty clear userland is up and copper stuff is down. Is USB even on the
same piece of paper?

There's no hope I can fix anything, but would be happy to test if it helps.

Thanks for reading!

bob prohaska