On Wed, May 03, 2017 at 11:38:09PM +0800, Ming Lei wrote: > On Wed, May 03, 2017 at 09:08:34AM -0600, Jens Axboe wrote: > > On 05/03/2017 09:03 AM, Ming Lei wrote: > > > On Wed, May 03, 2017 at 08:10:58AM -0600, Jens Axboe wrote: > > >> On 05/03/2017 08:08 AM, Jens Axboe wrote: > > >>> On 05/02/2017 10:03 PM, Ming Lei wrote: > > >>>> On Fri, Apr 28, 2017 at 02:29:18PM -0600, Jens Axboe wrote: > > >>>>> On 04/28/2017 09:15 AM, Ming Lei wrote: > > >>>>>> Hi, > > >>>>>> > > >>>>>> This patchset introduces flag of BLK_MQ_F_SCHED_USE_HW_TAG and > > >>>>>> allows to use hardware tag directly for IO scheduling if the queue's > > >>>>>> depth is big enough. In this way, we can avoid to allocate extra tags > > >>>>>> and request pool for IO schedule, and the schedule tag allocation/release > > >>>>>> can be saved in I/O submit path. > > >>>>> > > >>>>> Ming, I like this approach, it's pretty clean. It'd be nice to have a > > >>>>> bit of performance data to back up that it's useful to add this code, > > >>>>> though. Have you run anything on eg kyber on nvme that shows a > > >>>>> reduction in overhead when getting rid of separate scheduler tags? > > >>>> > > >>>> I can observe small improvement in the following tests: > > >>>> > > >>>> 1) fio script > > >>>> # io scheduler: kyber > > >>>> > > >>>> RWS="randread read randwrite write" > > >>>> for RW in $RWS; do > > >>>> echo "Running test $RW" > > >>>> sudo echo 3 > /proc/sys/vm/drop_caches > > >>>> sudo fio --direct=1 --size=128G --bsrange=4k-4k --runtime=20 --numjobs=1 --ioengine=libaio --iodepth=10240 --group_reporting=1 --filename=$DISK --name=$DISK-test-$RW --rw=$RW --output-format=json > > >>>> done > > >>>> > > >>>> 2) results > > >>>> > > >>>> --------------------------------------------------------- > > >>>> |sched tag(iops/lat) | use hw tag to sched(iops/lat) > > >>>> ---------------------------------------------------------- > > >>>> randread |188940/54107 | 193865/52734 > > >>>> ---------------------------------------------------------- > > >>>> read |192646/53069 | 199738/51188 > > >>>> ---------------------------------------------------------- > > >>>> randwrite |171048/59777 | 179038/57112 > > >>>> ---------------------------------------------------------- > > >>>> write |171886/59492 | 181029/56491 > > >>>> ---------------------------------------------------------- > > >>>> > > >>>> I guess it may be a bit more obvious when running the test on one slow > > >>>> NVMe device, and will try to find one and run the test again. > > >>> > > >>> Thanks for running that. As I said in my original reply, I think this > > >>> is a good optimization, and the implementation is clean. I'm fine with > > >>> the current limitations of when to enable it, and it's not like we > > >>> can't extend this later, if we want. > > >>> > > >>> I do agree with Bart that patch 1+4 should be combined. I'll do that. > > >> > > >> Actually, can you do that when reposting? Looks like you needed to > > >> do that anyway. > > > > > > Yeah, I will do that in V1. > > > > V2? :-) > > > > Sounds good. I just wanted to check the numbers here, with the series > > applied on top of for-linus crashes when switching to kyber. A few hunks > > Yeah, I saw that too, it has been fixed in my local tree, :-) > > > threw fuzz, but it looked fine to me. But I bet I fat fingered > > something. So it'd be great if you could respin against my for-linus > > branch. > > Actually, that is exactly what I am doing, :-) Looks v4.11 plus your for-linus often triggers the following hang during boot, and it seems caused by the change in (blk-mq: unify hctx delayed_run_work and run_work) UG: scheduling while atomic: kworker/0:1H/704/0x00000002 Modules linked in: Preemption disabled at: [<ffffffffaf5607bb>] virtio_queue_rq+0xdb/0x350 CPU: 0 PID: 704 Comm: kworker/0:1H Not tainted 4.11.0-04508-ga1f35f46164b #132 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.9.3-1.fc25 04/01/2014 Workqueue: kblockd blk_mq_run_work_fn Call Trace: dump_stack+0x65/0x8f ? virtio_queue_rq+0xdb/0x350 __schedule_bug+0x76/0xc0 __schedule+0x610/0x820 ? new_slab+0x2c9/0x590 schedule+0x40/0x90 schedule_timeout+0x273/0x320 ? ___slab_alloc+0x3cb/0x4f0 wait_for_completion+0x97/0x100 ? wait_for_completion+0x97/0x100 ? wake_up_q+0x80/0x80 flush_work+0x104/0x1a0 ? flush_workqueue_prep_pwqs+0x130/0x130 __cancel_work_timer+0xeb/0x160 ? vp_notify+0x16/0x20 ? virtqueue_add_sgs+0x23c/0x4a0 cancel_delayed_work_sync+0x13/0x20 blk_mq_stop_hw_queue+0x16/0x20 virtio_queue_rq+0x316/0x350 blk_mq_dispatch_rq_list+0x194/0x350 blk_mq_sched_dispatch_requests+0x118/0x170 ? finish_task_switch+0x80/0x1e0 __blk_mq_run_hw_queue+0xa3/0xc0 blk_mq_run_work_fn+0x2c/0x30 process_one_work+0x1e0/0x400 worker_thread+0x48/0x3f0 kthread+0x109/0x140 ? process_one_work+0x400/0x400 ? kthread_create_on_node+0x40/0x40 ret_from_fork+0x2c/0x40 Thansk, Ming
