Messages in this thread | | | Date | Tue, 18 Jun 2013 22:32:36 +0300 | Subject | Re: [PATCH v3 next/akpm] aio: convert the ioctx list to radix tree | From | Octavian Purdila <> |
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On Tue, Jun 18, 2013 at 10:08 PM, Benjamin LaHaise <bcrl@kvack.org> wrote: > On Tue, Jun 18, 2013 at 10:05:22PM +0300, Octavian Purdila wrote: >> On Fri, Jun 14, 2013 at 5:20 PM, Octavian Purdila >> <octavian.purdila@intel.com> wrote: >> > I picked up Ben's patch and incorporated Zach's idea and the first >> > results look promising, as expected. I am going to do a full test with >> > the same workload I've used for rbtree and come back with the results >> > and the patch in a day or so. >> > >> >> Unfortunately, I still see performance degradation for the one ioctx >> case even when using IDR. I am using the same fio benchmark as before. > > How much of a regression? >
Hi Ben,
It is even worse then radix, I've seen between 1% to even 4% degradation. I have tried to profile it and so far the culprit seems to be the hint code in idr_find. perf top -e dTLB-load-misses shows:
â static inline void *idr_find(struct idr *idr, int id) â { â struct idr_layer *hint = rcu_dereference_raw(idr->hint); â â if (hint && (id & ~IDR_MASK) == hint->prefix) â return rcu_dereference_raw(hint->ary[id & IDR_MASK]); 49.42 â d0: movzbl %r12b,%edx â add $0x4,%rdx â mov 0x8(%rax,%rdx,8),%rax
I should say that I am using kvm for testing this. Hopefully this is not a side effect of virtualization. I have attached the patch I am testing with.
Thanks, Tavi [unhandled content-type:application/octet-stream] | |