Messages in this thread | | | Subject | Re: [RFC] sched: Limit idle_balance() when it is being used too frequently | From | Jason Low <> | Date | Fri, 19 Jul 2013 12:15:18 -0700 |
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On Fri, 2013-07-19 at 20:37 +0200, Peter Zijlstra wrote: > On Thu, Jul 18, 2013 at 12:06:39PM -0700, Jason Low wrote: > > > N = 1 > > ----- > > 19.21% reaim [k] __read_lock_failed > > 14.79% reaim [k] mspin_lock > > 12.19% reaim [k] __write_lock_failed > > 7.87% reaim [k] _raw_spin_lock > > 2.03% reaim [k] start_this_handle > > 1.98% reaim [k] update_sd_lb_stats > > 1.92% reaim [k] mutex_spin_on_owner > > 1.86% reaim [k] update_cfs_rq_blocked_load > > 1.14% swapper [k] intel_idle > > 1.10% reaim [.] add_long > > 1.09% reaim [.] add_int > > 1.08% reaim [k] load_balance > > But but but but.. wth is causing this? The only thing we do more of with > N=1 is idle_balance(); where would that cause __{read,write}_lock_failed > and or mspin_lock() contention like that. > > There shouldn't be a rwlock_t in the entire scheduler; those things suck > worse than quicksand. > > If, as Rik thought, we'd have more rq->lock contention, then I'd > expected _raw_spin_lock to be up highest.
For this particular fserver workload, that mutex was acquired in the function calls from ext4_orphan_add() and ext4_orphan_del(). Those read and write lock calls were from start_this_handle().
Although these functions are not called within the idle_balance() code path, update_sd_lb_stats(), tg_load_down(), idle_cpu(), spin_lock(), ect... increases the time spent in the kernel and that appears to be indirectly causing more time to be spent acquiring those other kernel locks.
Thanks, Jason
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