On Mon, 15 Apr 2013 14:40:55 +0300 Octavian Purdila <octavian.purdila@xxxxxxxxx> wrote: > When using a large number of threads performing AIO operations the > IOCTX list may get a significant number of entries which will cause > significant overhead. For example, when running this fio script: > > rw=randrw; size=256k ;directory=/mnt/fio; ioengine=libaio; iodepth=1 > blocksize=1024; numjobs=512; thread; loops=100 > > on an EXT2 filesystem mounted on top of a ramdisk we can observe up to > 30% CPU time spent by lookup_ioctx: > > 32.51% [guest.kernel] [g] lookup_ioctx > 9.19% [guest.kernel] [g] __lock_acquire.isra.28 > 4.40% [guest.kernel] [g] lock_release > 4.19% [guest.kernel] [g] sched_clock_local > 3.86% [guest.kernel] [g] local_clock > 3.68% [guest.kernel] [g] native_sched_clock > 3.08% [guest.kernel] [g] sched_clock_cpu > 2.64% [guest.kernel] [g] lock_release_holdtime.part.11 > 2.60% [guest.kernel] [g] memcpy > 2.33% [guest.kernel] [g] lock_acquired > 2.25% [guest.kernel] [g] lock_acquire > 1.84% [guest.kernel] [g] do_io_submit > > This patchs converts the ioctx list to a radix tree. The patch looks nice. One thing we should pay attention to is the memory consumption. radix-trees can be far less space-efficient than lists, and as the tree key comes from mmap() it can be pretty sparsely distributed. So could you please have a think about this, see if we can cook up some worst-case numbers and decide if they are problematic? -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
