The following ktrace shows this:
c010a64d do_IRQ +<d/54> ( 0.39 ) ( 123767.76 ) pid(5392)
c010a1cf do_8259A_IRQ +<13/b4> ( 2.74 ) ( 123768.15 ) pid(5392)
c010a4f4 handle_IRQ_event +<10/78> ( 0.62 ) ( 123770.89 ) pid(5392)
c010e1ce timer_interrupt +<12/12c> ( 6.21 ) ( 123771.51) pid(5392)
c011418d do_timer +<d/5c> ( 1.20 ) ( 123777.72 ) pid(5392)
c010a109 enable_8259A_irq +<d/3c> ( 0.83 ) ( 123778.92 ) pid(5392)
c010a672 do_IRQ +<32/54> ( 0.13 ) ( 123779.75 ) pid(5392)
c011b630 do_bottom_half +<10/78> ( 0.14 ) ( 123779.88 ) pid(5392)
c010a68d do_IRQ +<4d/54> ( 1.19 ) ( 123780.02 ) pid(5392)
c0176841 tcp_send_delayed_ack +<d/60> ( 0.46 ) ( 123781.21 ) pid(5392)
c0112e7a add_timer +<e/190> ( 1.16 ) ( 123781.67 ) pid(5392)
c010a68d do_IRQ +<4d/54> ( 8294.68 ) ( 123782.83 ) pid(5392)
^^^----Ouch! Notice timer_bh is never run
until *after* the next timer_interrupt
c010a64d do_IRQ +<d/54> ( 0.44 ) ( 132077.51 ) pid(5392)
c010a1cf do_8259A_IRQ +<13/b4> ( 2.21 ) ( 132077.95 ) pid(5392)
c010a4f4 handle_IRQ_event +<10/78> ( 0.43 ) ( 132080.16 ) pid(5392)
c010e1ce timer_interrupt +<12/12c> ( 5.69 ) ( 132080.59 ) pid(5392)
c011418d do_timer +<d/5c> ( 0.77 ) ( 132086.28 ) pid(5392)
c010a109 enable_8259A_irq +<d/3c> ( 0.81 ) ( 132087.06 ) pid(5392)
c010a672 do_IRQ +<32/54> ( 0.13 ) ( 132087.86 ) pid(5392)
c011b630 do_bottom_half +<10/78> ( 0.66 ) ( 132087.99 ) pid(5392)
c0113e54 timer_bh +<10/33c> ( 0.77 ) ( 132088.65 ) pid(5392)
I set HZ=120 so it is reasonable for timer_interrupts to occur
at 8msec intervals. Also pid(5392) is set SCHED_FIFO and is
doing huge amounts of number crunching and hardly any system calls.
Many hours grepping and tracing kernel code has not revealed
the cause to me. Any ideas?
Wm
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