(no subject)

dieterbsd at engineer.com dieterbsd at engineer.com
Thu Apr 14 18:15:23 UTC 2011

[ Email attempt #3 and counting... ]

Alexander Motin wrote:
>> Warner Losh wrote:
>>> I don't suppose that your driver could cause the hardware to 
interrupt after a little time?  That would be more resource friendly... 
  Otherwise, 1ms is long enough that a msleep or tsleep would likely 
work quite nicely.
>> It's not his driver, it's mine. Actually, unlike AHCI, this hardware
>> even has interrupt for ready transition (second, biggest of sleeps). 
>> it is not used in present situation.
>>> On Apr 11, 2011, at 1:43 PM, dieterbsd at engineer.com wrote:
>>>>>> FreeBSD 8.2  amd64  uniprocessor
>>>>>> kernel: siisch1: DISCONNECT requested
>>>>>> kernel: siisch1: SIIS reset...
>>>>>> kernel: siisch1: siis_sata_connect() calling DELAY(1000)
>>>>>> last message repeated 59 times
>>>>>> kernel: siisch1: SATA connect time=60ms status=00000123
>>>>>> kernel: siisch1: SIIS reset done: devices=00000001
>>>>>> kernel: siisch1: DISCONNECT requested
>>>>>> kernel: siisch1: SIIS reset...
>>>>>> kernel: siisch1: siis_sata_connect() calling DELAY(1000)
>>>>>> last message repeated 58 times
>>>>>> kernel: siisch1: SATA connect time=59ms status=00000123
>>>>>> ...
>>>>>> kernel: siisch0: siis_wait_ready() calling DELAY(1000)
>>>>>> last message repeated 1300 times
>>>>>> kernel: siisch0: port is not ready (timeout 10000ms) status =
>>>> 001f2000
>>>>>> Meanwhile, *everything* comes to a screeching halt.  Device
>>>>>> drivers are locked out, and thus incoming data is lost.
>>>>>> Losing incoming data is unacceptable.
>>>>>> Need an alternative to DELAY() that does not lock out
>>>>>> other device drivers.  There must be a way to reset one
>>>>>> bit of hardware without locking down the entire machine.
>>>> Hans Petter Selasky writes:
>>>>> An alternative to DELAY() is the simplest solution. You probably 
>>>>> to do some redesign in the SCSI layer to find a better solution.
>>>> I keep coming back to the idea that a device driver for one
>>>> controller should not have to lock out *all* the hardware.
>>>> RS-232 locks out Ethernet.  Disk drivers lock out Ethernet.
>>>> And so on.  Why?  Is there some fundamental reason that this
>>>> *has* to be?  I thought the conversion from spl() to mutex()
>>>> was supposed to fix this?
>>>> I'm making progress on my project converting printf(9) calls
>>>> to log(9), and fixing some bugs along the way.  Eventually I'll
>>>> have patches to submit.  But this is really a workaround, not
>>>> a fix to the underlying problem.
>>>> Redesigning the SCSI layer sounds like a job for someone who took
>>>> a lot more CS classes than I did.  /dev/brain returns ENOCLUE.  :-(
>> CAM is not completely innocent in this situation indeed. CAM defines
>> XPT_RESET_BUS request as synchronous. It is not queued, and called 
>> the SIM mutex lock. I don't think lock can be safely dropped in the
>> middle there.
>> Now I think that I could try to move readiness waiting out of the
>> siis_reset() to do it asynchronously. I'll think about it.
> I've fixed this problem for ahci(4) in HEAD, there should be no sleeps
> longer then 100ms now (typical 1-2ms).
> With siis(4) the situation is different. There by default should be no
> sleeps longer then 100ms (typical 1-2ms). Longer sleep means that 
> controller is not responding, or it can't establish link to device it
> sees. I've reduced waiting timeout from 10s to 1s. It should improve
> situation a bit, but I would look for the original problem cause. Have
> you done something specific to trigger it? Are your drive/cables OK?

Thank you for your prompt attention to this problem, it is very much
appreciated.  (losing data sucks)

However, 100 ms is still way too long.  (assuming ms = milliseconds)
1 millisecond is dangerous, if Ethernet is locked out for approx 4
milliseconds there is guaranteed data loss.  I'd like to see
something more like 100 microseconds worst case (for TCP).  Closed
source closed hardware black box generates data, has a very small
output buffer, cannot be changed.  In some cases it insists on using
UDP rather than TCP so dropping even a single packet screws up the
data.  I have cranked the TCP and UDP receive buffer sizes way up,
I'm reading the ports at rtprio into a large buffer locked into main
memory, etc. etc.  Most of the time it works.

But if a device driver takes too long, incoming Ethernet packets do
not get serviced in time, and I lose data.  A device driver doing
printf(9) to the RS-232 console is too slow.  Changing printf to
log(9) works around this.  If a disk controller, port multiplier,
or disk has a hiccup, I lose data.  Siis(4) is the current problem,
but IIRC I've had problems from ahci(4) and ata(4) in the past.
I'm currently using all three drivers.

Is there any way I can keep the Ethernet from being locked out
by other drivers?

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