Large stack usage in fs code (especially for PPC64)

[Paul Mackerras]

Steven Rostedt writes:

> Here's my stack after boot up with CONFIG_IRQSTACKS set. Seems that 
> softirqs still use the same stack as the process.

They shouldn't.  I don't see do_softirq in the trace, though.  Which
functions did you think would be run in a softirq?  It looks to me
like the deepest 10 or so functions are called at hard irq level,
within hrtimer_interrupt called from timer_interrupt.

> root at electra ~> cat /debug/tracing/stack_trace 
>         Depth   Size      Location    (59 entries)
>         -----   ----      --------
>   0)    12384     192   ftrace_call+0x4/0x14
>   1)    12192     128   .sched_clock+0x20/0x60
>   2)    12064     128   .sched_clock_cpu+0x34/0x50
>   3)    11936     144   .cpu_clock+0x3c/0xa0
>   4)    11792     144   .get_timestamp+0x2c/0x50
>   5)    11648     144   .__touch_softlockup_watchdog+0x3c/0x60
>   6)    11504     192   .softlockup_tick+0xe4/0x220
>   7)    11312     128   .run_local_timers+0x34/0x50
>   8)    11184     160   .update_process_times+0x44/0xb0
>   9)    11024     176   .tick_sched_timer+0x8c/0x120
>  10)    10848     160   .__run_hrtimer+0xd8/0x130
>  11)    10688     240   .hrtimer_interrupt+0x16c/0x220
>  12)    10448     160   .timer_interrupt+0xcc/0x110
>  13)    10288      96   decrementer_common+0xe0/0x100

Paul.