Steve, You are totally correct. I used the wrong words when I said "ksoftirqd thread runs". My apologies for very misleading wording.
I have updated the wording in-line below, in the original message to indicate that it is softirq threads, in the ksoftirqd() function, not the ksoftirqd thread. -Frank -----Original Message----- From: Steven Rostedt [mailto:[EMAIL PROTECTED] Sent: Tue 1/15/2008 4:39 PM To: Rowand, Frank Cc: linux-kernel@vger.kernel.org; [EMAIL PROTECTED] Subject: Re: [PATCH] lost softirq, 2.6.24-rc7 On Tue, Jan 15, 2008 at 02:15:26PM -0800, Frank Rowand wrote: > From: Frank Rowand <[EMAIL PROTECTED]> > > (Ingo, there is a question for you after the description, just before the > patch.) > > When running an interrupt and network intensive stress test with PREEMPT_RT > enabled, the target system stopped processing received network packets. > skbs from received packets were being queued by net_rx_action(), but the > NET_RX_SOFTIRQ softirq was never running to remove the skbs from the queue. > Since the target system root file system is NFS mounted, the system is now > effectively hung. > > A pseudocode description of how this state was reached follows. > Each level of indentation represents a function call from the previous line. > > > ethernet driver irq handler receives packet > netif_rx() > queues skb (qlen == 1), raises NET_RX_SOFTIRQ > > on return from irq > ___do_softirq() [ 1 ] > Reset the pending bitmask Frank, This path should not be hit when running with PREEMPT_RT. The softirqs are now all separate, and are not run in batch in ksoftirqd. In fact, ksoftirqd should not be running at all with PREEMPT_RT. -- Steve > net_rx_action() > dequeues skb (qlen == 0) > jiffies incremented, so > break out of processing > and raise NET_RX_SOFTIRQ > (but don't deassert NAPI_STATE_SCHED) > > - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - > - > ksoftirqd thread runs ^^^^^^^^^^^^^^^^^^^^^^ should have been: the TIMER_SOFTIRQ and RCU_SOFTIRQ softirq threads, which are both executing ksoftirqd() run > process TIMER_SOFTIRQ > process RCU_SOFTIRQ > << ksoftirqd sleeps >> ^^^^^^^^^^^^^^^^^^^^^^^ should have been: the softirq threads, executing in ksoftirqd(), sleep > - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - > - > > ___do_softirq() [ 2 ] > Reset the pending bitmask > finds NET_RX_SOFTIRQ raised but already running > << ___do_softirq() [ 2 ] completes >> > > << ___do_softirq() [ 1 ] resumes >> > the pending bitmask is empty, so NET_RX_SOFTIRQ is lost > > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
