Messages in this thread | | | Date | Wed, 1 Feb 2006 18:24:13 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] Avoid moving tasks when a schedule can be made. |
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* Nick Piggin <nickpiggin@yahoo.com.au> wrote:
> >>But there are still places where interrupts can be held off for > >>indefinite periods. I don't see why the scheduler lock is suddenly > >>important [...] > > > > > >the scheduler lock is obviously important because it's the most central > >lock in existence. > > > > Now I call that argument much more illogical than any of mine. How can > such a fine grained, essentially per-cpu lock be "central", let alone > "most central"? [...]
i meant central in the sense that it's the most frequently taken lock, in the majority of workloads. Here's the output from the lock validator, sorted by number of ops per lock:
-> (dcache_lock){--} 124233 { -> (&rt_hash_locks[i]){-+} 131085 { -> (&dentry->d_lock){--} 312431 { -> (cpa_lock){++} 507385 { -> (__pte_lockptr(new)){--} 660193 { -> (kernel/synchro-test.c:&mutex){--} 825023 { -> (&rwsem){--} 930501 { -> (&rq->lock){++} 2029146 {
the runqueue lock is also central in the sense that it is the most spread-out lock in the locking dependencies graph. Toplist of locks, by number of backwards dependencies:
15 -> &cwq->lock 15 -> nl_table_wait 15 -> &zone->lock 17 -> &base->t_base.lock 32 -> modlist_lock 38 -> &cachep->spinlock 46 -> &parent->list_lock 47 -> &rq->lock
(obviously, as no other lock must nest inside the runqueue lock.)
so the quality of code (including asymptotic behavior) that runs under the runqueue lock is of central importance. I didnt think i'd ever have to explain this to you, but it is my pleasure to do so ;-) Maybe you thought of something else under "central"?
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