Re: [dm-devel] [RFC PATCH V2 3/3] dm: support bio polling

[Ming Lei <ming.lei@redhat.com>]

On Mon, Jun 21, 2021 at 07:33:34PM +0800, JeffleXu wrote:
> 
> 
> On 6/18/21 10:39 PM, Ming Lei wrote:
> > From 47e523b9ee988317369eaadb96826323cd86819e Mon Sep 17 00:00:00 2001
> > From: Ming Lei <ming.lei@redhat.com>
> > Date: Wed, 16 Jun 2021 16:13:46 +0800
> > Subject: [RFC PATCH V3 3/3] dm: support bio polling
> > 
> > Support bio(REQ_POLLED) polling in the following approach:
> > 
> > 1) only support io polling on normal READ/WRITE, and other abnormal IOs
> > still fallback on IRQ mode, so the target io is exactly inside the dm
> > io.
> > 
> > 2) hold one refcnt on io->io_count after submitting this dm bio with
> > REQ_POLLED
> > 
> > 3) support dm native bio splitting, any dm io instance associated with
> > current bio will be added into one list which head is bio->bi_end_io
> > which will be recovered before ending this bio
> > 
> > 4) implement .poll_bio() callback, call bio_poll() on the single target
> > bio inside the dm io which is retrieved via bio->bi_bio_drv_data; call
> > dec_pending() after the target io is done in .poll_bio()
> > 
> > 4) enable QUEUE_FLAG_POLL if all underlying queues enable QUEUE_FLAG_POLL,
> > which is based on Jeffle's previous patch.
> > 
> > Signed-off-by: Ming Lei <ming.lei@redhat.com>
> > ---
> > V3:
> > 	- covers all comments from Jeffle
> > 	- fix corner cases when polling on abnormal ios
> > 
> ...
> 
> One bug and one performance issue, though I haven't investigated deep
> for both.
> 
> 
> kernel base: based on Jens' for-next, applying Christoph and Leiming's
> patchset.
> 
> 
> 1. One bug when there's DM device stack, e.g., dm-linear upon another
> dm-linear. Can be reproduced by following steps:
> 
> ```
> $ sudo dmsetup create tmpdev --table '0 2097152 linear /dev/nvme0n1 0'
> 
> $ cat tmp.table
> 0 2097152 linear /dev/mapper/tmpdev 0
> 2097152 2097152 linear /dev/nvme0n1 0
> 
> $ cat tmp.table | dmsetup create testdev
> 
> $ fio -name=test -ioengine=io_uring -iodepth=128 -numjobs=1 -thread
> -rw=randread -direct=1 -bs=4k -time_based -runtime=10 -cpus_allowed=6
> -filename=/dev/mapper/testdev -hipri=1
> ```
> 
> 
> BUG: unable to handle page fault for address: ffffffffc01a6208
> #PF: supervisor write access in kernel mode
> #PF: error_code(0x0003) - permissions violation
> PGD 39740c067 P4D 39740c067 PUD 39740e067 PMD 1035db067 PTE 1ddf6f061
> Oops: 0003 [#1] SMP PTI
> CPU: 6 PID: 5899 Comm: fio Tainted: G S
> 5.13.0-0.1.git.81bcdc3.al7.x86_64 #1
> Hardware name: Inventec     K900G3-10G/B900G3, BIOS A2.20 06/23/2017
> RIP: 0010:dm_submit_bio+0x171/0x3e0 [dm_mod]
> Code: 08 85 c0 0f 84 78 01 00 00 80 7c 24 2c 00 0f 84 b8 00 00 00 48 8b
> 53 38 48 8b 44 24 18 48 85 d2 48 8d 48 28 48 89 50 28 74 04 <48> 89 4a
> 08 48 89 4b 38 48 83 c3 38 48 89 58 30 41 f7 c5 fe ff ff
> RSP: 0018:ffff9e5c45e1b9a0 EFLAGS: 00010286
> RAX: ffff8ab59fd50140 RBX: ffff8ab59fd50088 RCX: ffff8ab59fd50168
> RDX: ffffffffc01a6200 RSI: 0000000000052f08 RDI: 0000000000000000
> RBP: ffff8ab59fd501c8 R08: 0000000000000000 R09: 0000000000000000
> R10: ffff9e5c45e1b950 R11: 0000000000000007 R12: ffff8ab4c2bc2000
> R13: 0000000000000000 R14: ffff8ab4c2bc2548 R15: ffff8ab59fd50140
> FS:  00007f555de42700(0000) GS:ffff8af33f180000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: ffffffffc01a6208 CR3: 0000000124990005 CR4: 00000000003706e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  submit_bio_noacct+0x144/0x3f0
>  ? submit_bio+0x42/0x120
>  submit_bio+0x42/0x120
>  blkdev_direct_IO+0x454/0x4b0
>  ? io_resubmit_prep+0x40/0x40
>  ? __fsnotify_parent+0xff/0x350
>  ? __fsnotify_parent+0x10f/0x350
>  ? generic_file_read_iter+0x83/0x150
>  generic_file_read_iter+0x83/0x150
>  blkdev_read_iter+0x41/0x50
>  io_read+0xe9/0x420
>  ? __cond_resched+0x16/0x40
>  ? __kmalloc_node+0x16e/0x4e0
>  ? memcg_alloc_page_obj_cgroups+0x32/0x90
>  ? io_issue_sqe+0x7e8/0x1260
>  io_issue_sqe+0x7e8/0x1260
>  ? io_submit_sqes+0x47b/0x1420
>  __io_queue_sqe+0x56/0x380
>  ? io_submit_sqes+0x120a/0x1420
>  io_submit_sqes+0x120a/0x1420
>  ? __x64_sys_io_uring_enter+0x1d2/0x3e0
>  __x64_sys_io_uring_enter+0x1d2/0x3e0
>  ? exit_to_user_mode_prepare+0x4c/0x210
>  do_syscall_64+0x36/0x70
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
> RIP: 0033:0x7f55d3cb1b59
> Code: 00 f3 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89
> f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01
> f0 ff ff 73 01 c3 48 8b 0d ff e2 2b 00 f7 d8 64 89 01 48
> RSP: 002b:00007f555de41b18 EFLAGS: 00000246 ORIG_RAX: 00000000000001aa
> RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 00007f55d3cb1b59
> RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000005
> RBP: 00007f557ce81000 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000001 R11: 0000000000000246 R12: 0000000001276000
> R13: 0000000000000001 R14: 0000000000000000 R15: 00000000012c8328
> 
> 
> 
> 
> 2. Performance Issue
> 
> I test both on x86 (with only one NVMe) and aarch64 (with multiple NVMes).
> 
> The result (IOPS) on x86 is as expected:
> 
> Type 	  |IRQ   | Polling
> --------- | ---- | ----
> dm-linear | 239k | 357k
> 
> - dm-linear built upon one NVMe，bs=4k, iopoll=1, iodepth=128,
> numjobs=1, direct, randread, ioengine=io_uring
> 
> 
> 
> While the result on aarch64 is a little confusing.
> 
> Type 	      |IRQ   | Polling
> ------------- | ---- | ----
> dm-linear [1] | 208k | 230k
> dm-linear [2] | 637k | 691k
> dm-stripe     | 310k | 354k
> 
> - dm-linear [1] built upon *one* NVMe，bs=4k, iopoll=1, iodepth=128,
> *numjobs=1*, direct, randread, ioengine=io_uring
> - dm-linear [2] built upon *three* NVMes，bs=4k, iopoll=1, iodepth=128,
> *numjobs=3*, direct, randread, ioengine=io_uring
> - dm-stripe built upon *three* NVMes，chunk_size=4k, bs=12k, iopoll=1,
> iodepth=128, numjobs=3, direct, randread, ioengine=io_uring

Today I found the following patch makes a big difference on aarch64
nvme io polling, and you can try that in your test:

https://lore.kernel.org/linux-block/YNwfY6kExqJM65+L@T590/T/#m934fabf588d709109fd99040a3e26d7a9838db1f
https://lore.kernel.org/linux-block/YNwfY6kExqJM65+L@T590/T/#m4504b01d06566b2080216640625fac5fdd3929e5

BTW, my test machine is ampere(160cores, dual numa nodes).


Thanks,
Ming

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