High process latencies due to MPC5200 FEC hard- soft-irq processing
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From: Wolfgang Grandegger on 13 Jul 2010 09:30 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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |