Messages in this thread | | | Subject | Re: [thiscpuops upgrade 10/10] Lockless (and preemptless) fastpaths for slub | From | Peter Zijlstra <> | Date | Wed, 24 Nov 2010 18:26:50 +0100 |
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On Wed, 2010-11-24 at 10:14 -0600, Christoph Lameter wrote: > On Wed, 24 Nov 2010, Peter Zijlstra wrote: > > > This thing still relies on disabling IRQs in the slow path, which means > > its still going to be a lot of work to make it work on -rt. > > The disabling of irqs is because slab operations are used from interrupt > context. If we can avoid slab operations from interrupt contexts then we > can drop the interrupt disable in the slab allocators.
That's not so much the point, there's per-cpu assumptions due to that. Not everything is under a proper lock, see for example this bit:
new = new_slab(s, gfpflags, node);
if (gfpflags & __GFP_WAIT) local_irq_disable();
if (new) { c = __this_cpu_ptr(s->cpu_slab); stat(s, ALLOC_SLAB); if (c->page) flush_slab(s, c); slab_lock(new); __SetPageSlubFrozen(new); c->page = new; goto load_freelist; }
There we have the __this_cpu_ptr, c->page deref and flush_slab()->stat() call all before we take a lock.
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