Date:   Tue, 22 Jun 2021 09:08:43 +0200
From:   Paolo Valente <paolo.valente@...aro.org>
To:     Oleksandr Natalenko <oleksandr@...alenko.name>
Cc:     Jens Axboe <axboe@...nel.dk>,
        linux-block <linux-block@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Luca Mariotti <mariottiluca1@...mail.it>,
        Holger Hoffstätte <holger@...lied-asynchrony.com>,
        Pietro Pedroni <pedroni.pietro.96@...il.com>,
        Piotr Gorski <lucjan.lucjanov@...il.com>,
        Khazhy Kumykov <khazhy@...gle.com>, Jan Kara <jack@...e.cz>
Subject: Re: [PATCH FIXES/IMPROVEMENTS 0/7] block, bfq: preserve control,
 boost throughput, fix bugs

Hi,
CCing also Jan and Khazhy, because in your commit log I see also the
commit on bfq_requests_merged().

Is this OOPS reproducible for you?

Thanks,
Paolo


> Il giorno 21 giu 2021, alle ore 21:55, Oleksandr Natalenko <oleksandr@...alenko.name> ha scritto:
> 
> Hello.
> 
> On sobota 19. června 2021 16:09:41 CEST Paolo Valente wrote:
>> Hi Jens,
>> this series contains an already proposed patch by Luca, plus six new
>> patches. The goals of these patches are summarized in the subject of
>> this cover letter. I'm including Luca's patch here, because it enabled
>> the actual use of stable merge, and, as such, triggered an otherwise
>> silent bug. This series contains also the fix for that bug ("block,
>> bfq: avoid delayed merge of async queues"), tested by Holger [1].
>> 
>> Thanks,
>> Paolo
>> 
>> [1] https://lkml.org/lkml/2021/5/18/384
>> 
>> Luca Mariotti (1):
>>  block, bfq: fix delayed stable merge check
>> 
>> Paolo Valente (5):
>>  block, bfq: let also stably merged queues enjoy weight raising
>>  block, bfq: consider also creation time in delayed stable merge
>>  block, bfq: avoid delayed merge of async queues
>>  block, bfq: check waker only for queues with no in-flight I/O
>>  block, bfq: reset waker pointer with shared queues
>> 
>> Pietro Pedroni (1):
>>  block, bfq: boost throughput by extending queue-merging times
>> 
>> block/bfq-iosched.c | 68 +++++++++++++++++++++++++++++++++++----------
>> 1 file changed, 53 insertions(+), 15 deletions(-)
>> 
>> --
>> 2.20.1
> 
> Not sure everything goes fine here. After applying this series on top of the 
> latest stable 5.12 kernel I got this:
> 
> ```
> [16730.963248] kernel BUG at block/elevator.c:236!
> [16730.963254] invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
> [16730.963257] CPU: 11 PID: 109170 Comm: kworker/u64:5 Tainted: G        W         
> 5.12.0-pf7 #1
> [16730.963260] Hardware name: ASUS System Product Name/Pro WS X570-ACE, BIOS 
> 3601 05/26/2021
> [16730.963263] Workqueue: dm-thin do_worker [dm_thin_pool]
> [16730.963270] RIP: 0010:elv_rqhash_find+0xcc/0xd0
> [16730.963274] Code: 41 89 f0 81 e2 00 40 06 00 41 81 e0 1a 00 04 00 44 09 c2 
> 75 a9 be 09 00 00 00 c4 e2 4b f7 50 28 48 03 50 30 48 39 fa 75 c6 c3 <0f> 0b 
> 66 90 0f 1f 44 00 00 41 56 41 55 41 54 55 53 48 8b 47 68 48
> [16730.963276] RSP: 0018:ffffa558d13b7af8 EFLAGS: 00010046
> [16730.963279] RAX: ffff8a0007782d00 RBX: ffff8a0014b93000 RCX: ffffa558d13b7b78
> [16730.963281] RDX: ffff8a0014b93000 RSI: 0000000000063082 RDI: 000000001e0fdc00
> [16730.963283] RBP: ffff8a000731c770 R08: ffff8a000731c770 R09: fffffff0ffffddfb
> [16730.963284] R10: 0000000000000000 R11: 0000000000000400 R12: ffff8a0330365c00
> [16730.963286] R13: ffffa558d13b7b30 R14: 0000000000000000 R15: ffff8a0212fc4000
> [16730.963288] FS:  0000000000000000(0000) GS:ffff8a070ecc0000(0000) knlGS:
> 0000000000000000
> [16730.963290] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [16730.963292] CR2: 00007f1514d90f4c CR3: 0000000315952000 CR4: 
> 0000000000350ee0
> [16730.963294] Call Trace:
> [16730.963297]  elv_merge+0x96/0x120
> [16730.963300]  blk_mq_sched_try_merge+0x3e/0x370
> [16730.963303]  bfq_bio_merge+0xd3/0x130
> [16730.963306]  blk_mq_submit_bio+0x11e/0x6c0
> [16730.963309]  submit_bio_noacct+0x457/0x530
> [16730.963312]  raid10_unplug+0x13f/0x1a0 [raid10]
> [16730.963316]  blk_flush_plug_list+0xa9/0x110
> [16730.963319]  blk_finish_plug+0x21/0x30
> [16730.963322]  process_prepared_discard_passdown_pt1+0x204/0x2d0 
> [dm_thin_pool]
> [16730.963327]  do_worker+0x18e/0xce0 [dm_thin_pool]
> [16730.963335]  process_one_work+0x217/0x3e0
> [16730.963338]  worker_thread+0x4d/0x470
> [16730.963343]  kthread+0x182/0x1b0
> [16730.963349]  ret_from_fork+0x22/0x30
> …
> [16730.963419] ---[ end trace dd7e037f2028257b ]---
> [16730.963524] RIP: 0010:elv_rqhash_find+0xcc/0xd0
> …
> [16730.963547] note: kworker/u64:5[109170] exited with preempt_count 1
> [16747.948467] [drm:amdgpu_dm_atomic_commit_tail [amdgpu]] *ERROR* Waiting for 
> fences timed out!
> ```
> 
> Which is:
> 
> ```
> 229 struct request *elv_rqhash_find(struct request_queue *q, sector_t offset)
> 230 {
> …
> 235     hash_for_each_possible_safe(e->hash, rq, next, hash, offset) {
> 236         BUG_ON(!ELV_ON_HASH(rq));
> …
> ```
> 
> Yes, I carry some extra patches besides this series (the list is against v5.12 
> GA):
> 
> ```
> block, bfq: reset waker pointer with shared queues
> block, bfq: check waker only for queues with no in-flight I/O
> block, bfq: avoid delayed merge of async queues
> block, bfq: boost throughput by extending queue-merging times
> block, bfq: consider also creation time in delayed stable merge
> block, bfq: fix delayed stable merge check
> block, bfq: let also stably merged queues enjoy weight raising
> block: Do not pull requests from the scheduler when we cannot dispatch them
> blk: Fix lock inversion between ioc lock and bfqd lock
> bfq: Remove merged request already in bfq_requests_merged()
> block, bfq: avoid circular stable merges
> bfq: remove unnecessary BFQ_DEFAULT_GRP_IOPRIO
> bfq: reset entity->prio_changed in bfq_init_entity()
> bfq: optimize the calculation of bfq_weight_to_ioprio()
> bfq: remove unnecessary initialization logic
> bfq: keep the minimun bandwidth for CLASS_BE
> bfq: limit the IO depth of CLASS_IDLE to 1
> bfq: convert the type of bfq_group.bfqd to bfq_data*
> bfq: introduce bfq_entity_to_bfqg helper method
> bfq/mq-deadline: remove redundant check for passthrough request
> blk-mq: bypass IO scheduler's limit_depth for passthrough request
> block,bfq: fix the timeout calculation in bfq_bfqq_charge_time
> block, bfq: merge bursts of newly-created queues
> block, bfq: keep shared queues out of the waker mechanism
> block, bfq: fix weight-raising resume with !low_latency
> block, bfq: make shared queues inherit wakers
> block, bfq: put reqs of waker and woken in dispatch list
> block, bfq: always inject I/O of queues blocked by wakers
> ```
> 
> but nothing from there triggered this for quite some time.
> 
> Paolo, what do you think?
> 
> -- 
> Oleksandr Natalenko (post-factum)
> 
> 

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