Messages in this thread | | | Date | Tue, 13 Jul 2010 15:29:08 +0200 | From | Wolfgang Grandegger <> | Subject | High process latencies due to MPC5200 FEC hard- soft-irq processing |
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Hello,
we realized, that multiple ping floods (ping -f) can cause very large high-priority process latencies (up to a many seconds) on a MPC5200 PowerPC system with FEC NAPI support. The latencies are measured with
# cyclictest -p 80 -n
The problem is that processing of the ICMP pakets in the Hard-Irq and Soft-IRQ context can last for a long time without returning to the scheduler. Reducing MAX_SOFTIRQ_RESTART from 10 to 2 helps - the latency goes down to 35 ms with 2 "ping -f" - but it's not a configurable parameter, even if it somehow depends on the CPU power. And using the -rt patches seems overkill to me. Any other ideas or comments on how to get rid of such high process latencies?
Wolfgang.
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