[Soekris] net4826/TSC Bug

[Jim Cromie]

Chris Boot wrote:
> Aaron Isotton wrote:
>   
>> Chris Boot wrote:
>>     
>>> On 13 Jul 2006, at 22:30, Aaron Isotton wrote:
>>>
>>>       
>>>> Hi,
>>>>
>>>> I'm working with some net4826 boxes and I suspect that they are affected
>>>> by the TSC bug
>>>> (http://lists.soekris.com/pipermail/soekris-tech/2005-May/008432.html)
>>>> since they are based on the same processor as the 4801. Is that true?
>>>>         
>>> They are indeed.
>>>       
>> Ok, thanks.
>>
>>     
>>> 2.6.18 will have the new scx200_hrt Hi-Res timer code that works really
>>> rather nicely along with NTP. I didn't have too much trouble with my TSC
>>> while I was using that, however. If you want to use the Hi-Res timer
>>> just download 2.6.18-rc1. 
>>>       
You can also use 18-rc1 with either jiffies (but you dont want to..), or 
with the TSC. 

To use the TSC, pass 'idle=poll' on the command-line, this causes linux 
scheduler
to not 'halt' the machine when theres nothing to schedule, but instead 
to poll.
This will prevent entry into power-save modes, which is when the TSC stops.
Your box will run warmer this way though.


>> I don't so much care about NTP. What I do is analyzing TCP traffic and I
>> need high-resolution timestamps for that (I need resolutions of 0.1 ms
>> or less). Until now I was using the TSC for that because jiffies don't
>> have the resolution I need.
>>
>> Does this hi-res timer "magically fix" the TSC or do I have to use a
>> separate time source to use this scx200 timer?
>>     
>
> This is a separate time source, but it is built into the SC1200 CPU that the 
>   
sc-1100
> net48xx series use. However, as these aren't always that accurate I do suggest 
> you run ntpd which, with the new timesource code, will smooth out most 
> inaccuracies in time. I have no idea how accurate the timing is when passed back 
> to userspace mind you. The scx200_hrt ticks at either 1MHz or 27MHz.
>
>   
The new Timekeeping System in 18-rc1 keeps time in ns, and IIUC, all of 
that is available to userspace.
With this hires timer, the time quanta is 1000ns/27.

If you see oddities using the hrt, pls compare to tsc with/without 
idle=poll,
and let me know.

>>> If you get the latest git snapshot you'll also get my error LED code! :-D
>>>       
>> Now THAT'S what I call good news ;-)
>>     
>
> :-)
>
> Chris
>
>
>   
smiles all around
jimc