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Message-ID: <alpine.LFD.2.02.1106072345580.11814@ionos> Date: Tue, 7 Jun 2011 23:56:47 +0200 (CEST) From: Thomas Gleixner <tglx@...utronix.de> To: Tim Sander <tstone@...i.informatik.tu-darmstadt.de> cc: linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: Threaded Irqs (was "Changing Kernel thread priorities") On Tue, 7 Jun 2011, Tim Sander wrote: > Nevertheless are there still scheduling latencies for the usermode > handler thread which then runs at rt prio 99 for about 1ms. I know > this is not an preempt-rt kernel but i hoped to get better values out > of this configuration. > > So if anybody has an idea how to get better latencies out of a 2.6.39 > kernel, please let me know. The mainline forced irq thread handling is no guarantee for lower latencies. We need to disable preemption via local_bh_disable() for the forced threaded interrupts to satisfy the handler vs. softirq assumptions. So you might get long lasting preempt disabled regions due to long running interrupt handlers. Aside of that you still can get long periods due to code which runs with preemption or interrupts disabled. The forced threaded option has no way to change that. It would be interesting to find the root cause for those >1ms latencies. Tracing is your friend. Thanks, tglx -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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