CONFIG_PREEMPT_SOFTIRQS

CONFIG_PREEMPT_SOFTIRQS

[Vinod KK]

Hi,

I am using linux 2.6.10 (with Ingo Molnars real time patches) on my mips board.

When I try running high network traffic (10% traffic on a 100Mbps
link) on my target board with the CONFIG_PREEMPT_DESKTOP=y and
CONFIG_PREEMPT_SOFTIRQS=y options enabled I notice that the console
freezes and recovers only after the traffic stops. I do not notice
this behaviour with the CONFIG_PREEMPT_SOFTIRQS option disabled.

I understand that the CONFIG_PREEMPT_SOFTIRQS option puts all softirq
processing to the ksoftirqd daemon, but i do not see why this should
stall the console. I believe there should be some task which is
starving for CPU, but I do not know which one.

The console is on an 16550 serial port.

Could someone please give me some pointers on where I should start looking?

Thanks,
Vinod K.

Re: CONFIG_PREEMPT_SOFTIRQS

[Steven Rostedt]

On Tue, 2006-01-31 at 20:19 +0530, Vinod KK wrote:
> Hi,
> 
> I am using linux 2.6.10 (with Ingo Molnars real time patches) on my mips board.
> 
> When I try running high network traffic (10% traffic on a 100Mbps
> link) on my target board with the CONFIG_PREEMPT_DESKTOP=y and
> CONFIG_PREEMPT_SOFTIRQS=y options enabled I notice that the console
> freezes and recovers only after the traffic stops. I do not notice
> this behaviour with the CONFIG_PREEMPT_SOFTIRQS option disabled.
> 
> I understand that the CONFIG_PREEMPT_SOFTIRQS option puts all softirq
> processing to the ksoftirqd daemon, but i do not see why this should
> stall the console. I believe there should be some task which is
> starving for CPU, but I do not know which one.
> 
> The console is on an 16550 serial port.
> 
> Could someone please give me some pointers on where I should start looking?

2.6.10 with Ingo's patch is pretty old.  The -rt patch is very much a
moving target today and is not yet stable.  So the only real answer I
can give you is to go ahead and download
http://people.redhat.com/mingo/realtime-preempt/patch-2.6.15-rt16
and try that out.

-- Steve