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

Ming Lei
2018-03-29T09:40:21Z

On Thu, Mar 29, 2018 at 11:09:08AM +0200, Christian Borntraeger wrote:
>
>
> On 03/29/2018 09:23 AM, 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.
>
> FWIW, Limiting CONFIG_NR_CPUS to 64 seems to make the problem go away.

I think the following patch is needed, and this way aligns to the mapping
created via managed IRQ at least.

diff --git a/block/blk-mq-cpumap.c b/block/blk-mq-cpumap.c
index 9f8cffc8a701..638ab5c11b3c 100644
--- a/block/blk-mq-cpumap.c
+++ b/block/blk-mq-cpumap.c
@@ -14,13 +14,12 @@
#include "blk.h"
#include "blk-mq.h"

+/*
+ * Given there isn't CPU hotplug handler in blk-mq, map all possible CPUs to
+ * queues even it isn't present yet.
+ */
static int cpu_to_queue_index(unsigned int nr_queues, const int cpu)
{
- /*
- * Non present CPU will be mapped to queue index 0.
- */
- if (!cpu_present(cpu))
- return 0;
return cpu % nr_queues;
}

Thanks,
Ming