On Wed, Mar 13, 2013 at 02:28:02PM -0700, Paul E. McKenney wrote: > On Wed, Mar 13, 2013 at 05:03:07PM -0400, Paul Gortmaker wrote: > > [Re: Threaded irqs + 100% CPU RT task = RCU stall] On 06/03/2013 (Wed 13:45) Paul E. McKenney wrote: > > > > [...] > > > > > > > > Is this behavior OK? If so, the following (untested) patch might do > > > what you want. ;-) > > > > > > Thanx, Paul > > > > > > ------------------------------------------------------------------------ > > > > > > rcu: Add softirq-stall indications to stall-warning messages > > > > [...] > > > > > > > > +The "softirq=" portion of the message tracks the number of RCU softirq > > > +handlers that the stalled CPU has executed. The number before the "/" > > > +is the number that had executed since boot at the time that this CPU > > > +last noted the beginning of a grace period, which might be the current > > > +(stalled) grace period, or it might be some earlier grace period (for > > > +example, if the CPU might have been in dyntick-idle mode for an extended > > > +time period. The number after the "/" is the number that have executed > > > +since boot until the current time. If this latter number stays constant > > > +across repeated stall-warning messages, it is possible that RCU's softirq > > > +handlers are no longer able to execute on this CPU. This can happen if > > > +the stalled CPU is spinning with interrupts are disabled, or, in -rt > > > +kernels, if a high-priority process is starving RCU's softirq handler. > > > > Here is the output of two consecutive stalls (triggered exactly as I'd > > described before) after applying the commit and enabling the new config > > option for RCU_CPU_STALL_INFO (btw, do we need this? we already have > > the RCU_CPU_STALL_VERBOSE option, and the distinction isn't clear.) I won't argue that the choice of names is particularly inspired. RCU_CPU_STALL_VERBOSE prints per-task information for any tasks stalling the current RCU grace period. RCU_CPU_STALL_INFO prints additional debug info for each CPU. Perhaps I should merge them or rename them. I will give it some thought. Thanx, Paul > > Looking at the output, it doesn't necessarily scream out "you are an > > idiot" in a way that Joe Average can immediately parse and understand, > > but I guess it does at least arm us with more information so that we > > can tell Joe Average that he is an idiot (assuming he posts more than > > just a single stall instance). > > OK, will queue this patch for 3.10, then, with your Tested-by. > > > Also note right after the <EOI> below, it looks like two stall > > messages got interleavedi, or a carriage return got dropped... > > (not suggesting that this patch caused that.). > > No idea... Will recheck synchronization. Oh, wait... The stall warnings > for self-detected stalls are not synchronized. This is a tradeoff. > If I synchronize them, and there are multiple CPUs stalling concurrently > and self-detecting those stalls, then I randomly lose stalls from some > of the CPUs. I could let the winner complain on behalf of all currently > stalled CPUs, but remote stack tracing is inaccurate. > > My thought is to leave it, unless someone has a cute idea for making it > all work nicely. > > Thanx, Paul > > > Paul. > > -- > > > > INFO: rcu_preempt self-detected stall on CPU > > INFO: rcu_preempt detected stalls on CPUs/tasks: > > 1: (1 GPs behind) idle=f4f/140000000000001/0 softirq=2256/2257 > > (detected by 5, t=60002 jiffies, g=324, c=323, q=1368) > > Task dump for CPU 1: > > eatme-simple R running task 0 1487 1433 0x00000000 > > ffff88042ef47f60 ffffffff81316de1 ffff88042e5f5810 ffff88042ef47fd8 > > 0000000000010c00 ffff88042ef47fd8 ffff88042f994210 ffff88042e5f5810 > > 0000000000000000 ffff88043f4fe980 ffffffff810a56e4 0000000000000203 > > Call Trace: > > [<ffffffff81316de1>] ? __schedule+0x62a/0x75e > > [<ffffffff810a56e4>] ? dput+0x20/0x15c > > [<ffffffff81096070>] ? __fput+0x1a1/0x1c8 > > [<ffffffff810ab833>] ? mntput_no_expire+0x13/0x11f > > [<ffffffff8101c55c>] ? do_page_fault+0x1f/0x3b > > > > 1: (1 GPs behind) idle=f4f/140000000000001/0 softirq=2256/2257 > > (t=60082 jiffies g=324 c=323 q=1368) > > Pid: 1487, comm: eatme-simple Not tainted 3.9.0-rc2+ #2 > > Call Trace: > > <IRQ> [<ffffffff8105cac6>] ? rcu_check_callbacks+0x215/0x61a > > [<ffffffff8102cffc>] ? update_process_times+0x31/0x5c > > [<ffffffff8104bb5b>] ? tick_handle_periodic+0x18/0x52 > > [<ffffffff81016328>] ? smp_apic_timer_interrupt+0x7d/0x8f > > [<ffffffff8131944a>] ? apic_timer_interrupt+0x6a/0x70 > > <EOI> > > INFO: rcu_preempt self-detected stall on CPUINFO: rcu_preempt detected stalls on CPUs/tasks: > > 1: (1 GPs behind) idle=f4f/140000000000001/0 softirq=2256/2257 > > (detected by 5, t=240007 jiffies, g=324, c=323, q=9386) > > Task dump for CPU 1: > > eatme-simple R running task 0 1487 1433 0x00000000 > > ffff88042ef47f60 ffffffff81316dfd ffff88042e5f5810 ffff88042ef47fd8 > > 0000000000010c00 ffff88042ef47fd8 ffff88042e5f5810 ffff88042e5f5810 > > 0000000000000000 ffff88043f4fe980 ffffffff810a56e4 0000000000000203 > > Call Trace: > > [<ffffffff81316dfd>] ? __schedule+0x646/0x75e > > [<ffffffff810a56e4>] ? dput+0x20/0x15c > > [<ffffffff81096070>] ? __fput+0x1a1/0x1c8 > > [<ffffffff810ab833>] ? mntput_no_expire+0x13/0x11f > > [<ffffffff8101c55c>] ? do_page_fault+0x1f/0x3b > > > > 1: (1 GPs behind) idle=f4f/140000000000001/0 softirq=2256/2257 > > (t=240087 jiffies g=324 c=323 q=9386) > > Pid: 1487, comm: eatme-simple Not tainted 3.9.0-rc2+ #2 > > Call Trace: > > <IRQ> [<ffffffff8105cac6>] ? rcu_check_callbacks+0x215/0x61a > > [<ffffffff8102cffc>] ? update_process_times+0x31/0x5c > > [<ffffffff8104bb5b>] ? tick_handle_periodic+0x18/0x52 > > [<ffffffff81016328>] ? smp_apic_timer_interrupt+0x7d/0x8f > > [<ffffffff8131944a>] ? apic_timer_interrupt+0x6a/0x70 > > -- 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
