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SubjectRe: sched: context tracking demolishes pipe-test
On Sun, Jun 30, 2013 at 09:57:36AM +0200, Mike Galbraith wrote:
> taskset -c 3 pipe-test 1
>
> switch-rate
> 3.10.0-master 426.4 KHz
> 3.10.0-masterx 591.8 Khz 1.387 (591=notgood, 426=omfg)
>
> 3.10.0-master 3.10.0-masterx
> 7.13% [k] __schedule 9.58% [k] __schedule
> ! 6.02% [.] __read_nocancel 8.25% [k] system_call
> ! 5.82% [.] __write_nocancel 5.34% [k] _raw_spin_lock_irqsave
> ! 4.28% [k] system_call 4.26% [k] pipe_read
> ! 4.13% [k] user_exit 3.53% [k] copy_user_generic_string
> 3.64% [k] _raw_spin_lock_irqsave 3.52% [k] native_sched_clock
> 3.37% [k] pipe_read 3.43% [k] __switch_to
> 2.72% [k] copy_user_generic_string 3.21% [.] main
> 2.60% [.] main 2.96% [k] mutex_lock
> 2.59% [k] native_sched_clock 2.89% [k] mutex_unlock
> 2.47% [k] __switch_to 2.86% [k] sched_clock_local
> 2.10% [k] mutex_unlock 2.63% [.] __read_nocancel
> 2.08% [k] sched_clock_local 2.47% [k] pipe_write
> 2.05% [k] mutex_lock 2.37% [k] _raw_spin_unlock_irqrestore
> 1.91% [k] pipe_write 1.96% [.] __write_nocancel
> 1.89% [k] user_enter 1.62% [k] vfs_write
> 1.72% [k] _raw_spin_unlock_irqrestore 1.54% [k] do_sync_write
> 1.51% [k] rcu_eqs_enter_common.isra.47 1.52% [k] fget_light
> 1.41% [k] rcu_eqs_exit_common.isra.45 1.48% [k] fsnotify
> 1.30% [k] tracesys 1.39% [k] dequeue_task_fair
> 1.23% [k] fsnotify 1.39% [k] update_curr
> 1.23% [k] int_check_syscall_exit_worka 1.37% [k] do_sync_read
> 1.20% [k] fget_light 1.33% [.] __GI___libc_write
> 1.16% [k] vfs_write 1.29% [k] try_to_wake_up
> 1.05% [k] syscall_trace_enter 1.09% [k] _raw_spin_lock_irq
> 1.04% [k] do_sync_write 1.08% [k] pipe_iov_copy_from_user
> 1.03% [k] context_tracking_task_switch 1.05% [k] finish_task_switch
> 0.99% [k] update_curr 1.04% [k] prepare_to_wait
>

Yeah, who'd have thought that putting stuff in the syscall path would've
made syscalls more expensive ;-)

But yeah, that's a _lot_ more expensive.. I'd not be surprised if more
people would find that objectionable.


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