Hi Thomas/Anna/John, Recently I found that the hrtimer become inaccurate when there is a RT process runs on the same cpu core, and the kernel has applied preempt_rt patch. The Linux kernel version is v4.1.46, and the preempt_rt patch is patch-4.1.46-rt52.patch. I know that in the preempt_rt environment the interrupt handlers no longer run in interrupt context but in process context, so that RT process will not be interrupt. But if the hrtimer is also runs in process context the timer is useless when it's inaccurate. so I want to consult you whether this is expected behavior? whether is reasonable to move the timer IRQ handling to a thread? Check the patch-4.1.46-rt52.patch will found in function 'hrtimer_interrupt' the modify below: @@ -1296,7 +1539,10 @@ retry: if (basenow.tv64 < hrtimer_get_softexpires_tv64(timer)) break; - __run_hrtimer(timer, &basenow); + if (!hrtimer_rt_defer(timer)) + __run_hrtimer(timer, &basenow); + else + raise = 1; } } /* Reevaluate the clock bases for the next expiry */ @@ -1357,6 +1603,9 @@ retry: tick_program_event(expires_next, 1); printk_once(KERN_WARNING "hrtimer: interrupt took %llu ns\n", ktime_to_ns(delta)); +out: + if (raise) + raise_softirq_irqoff(HRTIMER_SOFTIRQ); } I think this is why hrtimer is run as a thread, I tried to set hrtimer.irqsafe to 1, but the timer still seemed not right. Could anyone give some advise? Thanks. -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
