Re: [PATCH] blk-mq: only run mapped hw queues in blk_mq_run_hw_queues()

Ming Lei
2018-03-29T10:13:21Z

On Thu, Mar 29, 2018 at 05:52:16PM +0800, Ming Lei wrote:
> On Thu, Mar 29, 2018 at 09:23:10AM +0200, Christian Borntraeger wrote:
> >
> >
> > On 03/29/2018 04:00 AM, Ming Lei wrote:
> > > On Wed, Mar 28, 2018 at 05:36:53PM +0200, Christian Borntraeger wrote:
> > >>
> > >>
> > >> On 03/28/2018 05:26 PM, Ming Lei wrote:
> > >>> Hi Christian,
> > >>>
> > >>> On Wed, Mar 28, 2018 at 09:45:10AM +0200, Christian Borntraeger wrote:
> > >>>> FWIW, this patch does not fix the issue for me:
> > >>>>
> > >>>> ostname=? addr=? terminal=? res=success'
> > >>>> [ 21.454961] WARNING: CPU: 3 PID: 1882 at block/blk-mq.c:1410 __blk_mq_delay_run_hw_queue+0xbe/0xd8
> > >>>> [ 21.454968] Modules linked in: scsi_dh_rdac scsi_dh_emc scsi_dh_alua dm_mirror dm_region_hash dm_log dm_multipath dm_mod autofs4
> > >>>> [ 21.454984] CPU: 3 PID: 1882 Comm: dasdconf.sh Not tainted 4.16.0-rc7+ #26
> > >>>> [ 21.454987] Hardware name: IBM 2964 NC9 704 (LPAR)
> > >>>> [ 21.454990] Krnl PSW : 00000000c0131ea3 000000003ea2f7bf (__blk_mq_delay_run_hw_queue+0xbe/0xd8)
> > >>>> [ 21.454996] R:0 T:1 IO:0 EX:0 Key:0 M:1 W:0 P:0 AS:3 CC:0 PM:0 RI:0 EA:3
> > >>>> [ 21.455005] Krnl GPRS: 0000013abb69a000 0000013a00000000 0000013ac6c0dc00 0000000000000001
> > >>>> [ 21.455008] 0000000000000000 0000013abb69a710 0000013a00000000 00000001b691fd98
> > >>>> [ 21.455011] 00000001b691fd98 0000013ace4775c8 0000000000000001 0000000000000000
> > >>>> [ 21.455014] 0000013ac6c0dc00 0000000000b47238 00000001b691fc08 00000001b691fbd0
> > >>>> [ 21.455032] Krnl Code: 000000000069c596: ebaff0a00004 lmg %r10,%r15,160(%r15)
> > >>>> 000000000069c59c: c0f4ffff7a5e brcl 15,68ba58
> > >>>> #000000000069c5a2: a7f40001 brc 15,69c5a4
> > >>>> >000000000069c5a6: e340f0c00004 lg %r4,192(%r15)
> > >>>> 000000000069c5ac: ebaff0a00004 lmg %r10,%r15,160(%r15)
> > >>>> 000000000069c5b2: 07f4 bcr 15,%r4
> > >>>> 000000000069c5b4: c0e5fffffeea brasl %r14,69c388
> > >>>> 000000000069c5ba: a7f4fff6 brc 15,69c5a6
> > >>>> [ 21.455067] Call Trace:
> > >>>> [ 21.455072] ([<00000001b691fd98>] 0x1b691fd98)
> > >>>> [ 21.455079] [<000000000069c692>] blk_mq_run_hw_queue+0xba/0x100
> > >>>> [ 21.455083] [<000000000069c740>] blk_mq_run_hw_queues+0x68/0x88
> > >>>> [ 21.455089] [<000000000069b956>] __blk_mq_complete_request+0x11e/0x1d8
> > >>>> [ 21.455091] [<000000000069ba9c>] blk_mq_complete_request+0x8c/0xc8
> > >>>> [ 21.455103] [<00000000008aa250>] dasd_block_tasklet+0x158/0x490
> > >>>> [ 21.455110] [<000000000014c742>] tasklet_hi_action+0x92/0x120
> > >>>> [ 21.455118] [<0000000000a7cfc0>] __do_softirq+0x120/0x348
> > >>>> [ 21.455122] [<000000000014c212>] irq_exit+0xba/0xd0
> > >>>> [ 21.455130] [<000000000010bf92>] do_IRQ+0x8a/0xb8
> > >>>> [ 21.455133] [<0000000000a7c298>] io_int_handler+0x130/0x298
> > >>>> [ 21.455136] Last Breaking-Event-Address:
> > >>>> [ 21.455138] [<000000000069c5a2>] __blk_mq_delay_run_hw_queue+0xba/0xd8
> > >>>> [ 21.455140] ---[ end trace be43f99a5d1e553e ]---
> > >>>> [ 21.510046] dasdconf.sh Warning: 0.0.241e is already online, not configuring
> > >>>
> > >>> Thinking about this issue further, I can't understand the root cause for
> > >>> this issue.
> > >>>
> > >>> After commit 20e4d813931961fe ("blk-mq: simplify queue mapping & schedule with
> > >>> each possisble CPU"), each hw queue should be mapped to at least one CPU, that
> > >>> means this issue shouldn't happen. Maybe blk_mq_map_queues() works wrong?
> > >>>
> > >>> Could you dump 'lscpu' and provide blk-mq debugfs for your DASD via the
> > >>> following command?
> > >>
> > >> # lscpu
> > >> Architecture: s390x
> > >> CPU op-mode(s): 32-bit, 64-bit
> > >> Byte Order: Big Endian
> > >> CPU(s): 16
> > >> On-line CPU(s) list: 0-15
> > >> Thread(s) per core: 2
> > >> Core(s) per socket: 8
> > >> Socket(s) per book: 3
> > >> Book(s) per drawer: 2
> > >> Drawer(s): 4
> > >> NUMA node(s): 1
> > >> Vendor ID: IBM/S390
> > >> Machine type: 2964
> > >> CPU dynamic MHz: 5000
> > >> CPU static MHz: 5000
> > >> BogoMIPS: 20325.00
> > >> Hypervisor: PR/SM
> > >> Hypervisor vendor: IBM
> > >> Virtualization type: full
> > >> Dispatching mode: horizontal
> > >> L1d cache: 128K
> > >> L1i cache: 96K
> > >> L2d cache: 2048K
> > >> L2i cache: 2048K
> > >> L3 cache: 65536K
> > >> L4 cache: 491520K
> > >> NUMA node0 CPU(s): 0-15
> > >> Flags: esan3 zarch stfle msa ldisp eimm dfp edat etf3eh highgprs te vx sie
> > >>
> > >> # lsdasd
> > >> Bus-ID Status Name Device Type BlkSz Size Blocks
> > >> ==============================================================================
> > >> 0.0.3f75 active dasda 94:0 ECKD 4096 21129MB 5409180
> > >> 0.0.3f76 active dasdb 94:4 ECKD 4096 21129MB 5409180
> > >> 0.0.3f77 active dasdc 94:8 ECKD 4096 21129MB 5409180
> > >> 0.0.3f74 active dasdd 94:12 ECKD 4096 21129MB 5409180
> > >
> > > I have tried to emulate your CPU topo via VM and the blk-mq mapping of
> > > null_blk is basically similar with your DASD mapping, but still can't
> > > reproduce your issue.
> > >
> > > BTW, do you need to do cpu hotplug or other actions for triggering this warning?
> >
> > No, without hotplug.
>
> From the debugfs log, hctx0 is mapped to lots of CPU, so it shouldn't be
> unmapped, could you check if it is hctx0 which is unmapped when the
> warning is triggered? If not, what is the unmapped hctx? And you can do
> that by adding one extra line:
>
> printk("unmapped hctx %d", hctx->queue_num);

It should be triggered when running any hctx from 16 to 63, instead of
0.

I see why I didn't trigger it via null_blk, because null_blk won't run
all hw queues, and I should have used scsi_debug to do that.

Then the patch of touching blk-mq-cpumap.c I sent before should address
this issue.

Thanks,
Ming