On Thu, Mar 19, 2015 at 2:28 AM, Maxim Patlasov <[email protected]> wrote: > On 01/13/2015 07:44 AM, Ming Lei wrote: >> >> Part of the patch is based on Dave's previous post. >> >> This patch submits I/O to fs via kernel aio, and we >> can obtain following benefits: >> >> - double cache in both loop file system and backend file >> gets avoided >> - context switch decreased a lot, and finally CPU utilization >> is decreased >> - cached memory got decreased a lot >> >> One main side effect is that throughput is decreased when >> accessing raw loop block(not by filesystem) with kernel aio. >> >> This patch has passed xfstests test(./check -g auto), and >> both test and scratch devices are loop block, file system is ext4. >> >> Follows two fio tests' result: >> >> 1. fio test inside ext4 file system over loop block >> 1) How to run >> - linux kernel base: 3.19.0-rc3-next-20150108(loop-mq merged) >> - loop over SSD image 1 in ext4 >> - linux psync, 16 jobs, size 200M, ext4 over loop block >> - test result: IOPS from fio output >> >> 2) Throughput result: >> ------------------------------------------------------------- >> test cases |randread |read |randwrite |write | >> ------------------------------------------------------------- >> base |16799 |59508 |31059 |58829 >> ------------------------------------------------------------- >> base+kernel aio |15480 |64453 |30187 |57222 >> ------------------------------------------------------------- > > > Ming, it's important to understand the overhead of aio_kernel_() > implementation. So could you please add test results for raw SSD device to > the table above next time (in v3 of your patches).
what aio_kernel_() does is to just call ->read_iter()/->write_iter(), so it should not have introduced extra overload. >From performance view, the effect is only from switching to O_DIRECT. With O_DIRECT, double cache can be avoided, meantime both page caches and CPU utilization can be decreased. V3 need to rewrite against recent vfs's change(in -next already) about splitting kiocb patches, and thanks to Christoph's patches, aio_kernel_() can be implemented just inside loop and it may become a bit simple. > > Jens, if you have some fast storage at hand, could you please measure IOPS > for Ming's patches vs. raw block device -- to ensure that the patches do not > impose too low limit on performance. > > Thanks, > Maxim -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
