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[ts-7000] Re: Sub 10ms delay on TS-7552 (Cavium cpu)

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Subject: [ts-7000] Re: Sub 10ms delay on TS-7552 (Cavium cpu)
From: "Kris" <>
Date: Tue, 06 Jul 2010 21:03:47 -0000
These are all artifacts from changing your kernel tick rate.  The booting delay 
seen by SD card is because you are causing context switching to happen more 
often (every 1ms as opposed to 10ms) and since sdctl and nbd are userspace 
applications they can get switched out more if the dynamic scheduler of the 
kernel feels they are getting too much CPU time.

The BoGoMIPS is calibrated based on the kernel tick I believe.  They are a 
horribly measure of CPU speed anyway, and messing with the tick times 10 threw 
off the calculation times 10.  

-Kris Bahnsen
Technologic Systems


--- In  JF Morneau <> wrote:
>
> With the default kernel, I can't get delays of less than 10ms. I 
> increased the CONFIG_HZ from 100 to 1000 and I now can get sub 10ms delays.
> 
> Timing in our program seems to work. I could verify from an external 
> time source that a 2 ms delay is really 2 ms. However, our custom setup 
> was booting in around 13 sec from sd.  It now boots in 30 sec. I also 
> noticed this change from dmesg:
> 
> [    0.020000] Calibrating delay loop (skipped)... 1916.92 BogoMIPS preset
> 
> Before, it was:
> 
> [    0.010000] Calibrating delay loop (skipped)... 191.69 BogoMIPS preset
> 
> It seems that there is more to it than just changing the CONFIG_HZ 
> kernel config.
>




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