On 12/04/2014 07:57 PM, Tejun Heo wrote: > Hello, > > On Wed, Dec 03, 2014 at 12:33:59AM +0200, Leonard Crestez wrote: >> It seems that free_percpu performance is very bad when working with small >> objects. The easiest way to reproduce this is to allocate and then free a >> large >> number of percpu int counters in order. Small objects (reference counters >> and >> pointers) are common users of alloc_percpu and I think this should be fast. >> This particular issue can be encountered with very large number of net_device >> structs. > > Do you actually experience this with an actual workload? The thing is > allocation has the same quadratic complexity. If this is actually an > issue (which can definitely be the case), I'd much prefer implementing > a properly scalable area allocator than mucking with the current > implementation.
Yes, we are actually experiencing issues with this. We create lots of virtual net_devices and routes, which means lots of percpu counters/pointers. In particular we are getting worse performance than in older kernels because the net_device refcnt is now a percpu counter. We could turn that back into a single integer but this would negate an upstream optimization. We are working on top of linux_3.10. We already pulled some allocation optimizations. At least for simple allocation patterns pcpu_alloc does not appear to be unreasonably slow. Having a "properly scalable" percpu allocator would be quite nice indeed. Regards, Leonard -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
