RE: Re: [PATCH v29 4/4] scsi: ufs: Add HPB 2.0 support

[Daejun Park <daejun7.park@samsung.com>]

>On 2021-03-17 09:42, Daejun Park wrote:
>>> On 2021-03-15 15:23, Can Guo wrote:
>>>> On 2021-03-15 15:07, Daejun Park wrote:
>>>>>>> This patch supports the HPB 2.0.
>>>>>>> 
>>>>>>> The HPB 2.0 supports read of varying sizes from 4KB to 512KB.
>>>>>>> In the case of Read (<= 32KB) is supported as single HPB read.
>>>>>>> In the case of Read (36KB ~ 512KB) is supported by as a 
>>>>>>> combination
>>>>>>> of
>>>>>>> write buffer command and HPB read command to deliver more PPN.
>>>>>>> The write buffer commands may not be issued immediately due to 
>>>>>>> busy
>>>>>>> tags.
>>>>>>> To use HPB read more aggressively, the driver can requeue the 
>>>>>>> write
>>>>>>> buffer
>>>>>>> command. The requeue threshold is implemented as timeout and can 
>>>>>>> be
>>>>>>> modified with requeue_timeout_ms entry in sysfs.
>>>>>>> 
>>>>>>> Signed-off-by: Daejun Park <daejun7.park@samsung.com>
>>>>>>> ---
>>>>>>> +static struct attribute *hpb_dev_param_attrs[] = {
>>>>>>> +        &dev_attr_requeue_timeout_ms.attr,
>>>>>>> +        NULL,
>>>>>>> +};
>>>>>>> +
>>>>>>> +struct attribute_group ufs_sysfs_hpb_param_group = {
>>>>>>> +        .name = "hpb_param_sysfs",
>>>>>>> +        .attrs = hpb_dev_param_attrs,
>>>>>>> +};
>>>>>>> +
>>>>>>> +static int ufshpb_pre_req_mempool_init(struct ufshpb_lu *hpb)
>>>>>>> +{
>>>>>>> +        struct ufshpb_req *pre_req = NULL;
>>>>>>> +        int qd = hpb->sdev_ufs_lu->queue_depth / 2;
>>>>>>> +        int i, j;
>>>>>>> +
>>>>>>> +        INIT_LIST_HEAD(&hpb->lh_pre_req_free);
>>>>>>> +
>>>>>>> +        hpb->pre_req = kcalloc(qd, sizeof(struct ufshpb_req),
>>>>>>> GFP_KERNEL);
>>>>>>> +        hpb->throttle_pre_req = qd;
>>>>>>> +        hpb->num_inflight_pre_req = 0;
>>>>>>> +
>>>>>>> +        if (!hpb->pre_req)
>>>>>>> +                goto release_mem;
>>>>>>> +
>>>>>>> +        for (i = 0; i < qd; i++) {
>>>>>>> +                pre_req = hpb->pre_req + i;
>>>>>>> +                INIT_LIST_HEAD(&pre_req->list_req);
>>>>>>> +                pre_req->req = NULL;
>>>>>>> +                pre_req->bio = NULL;
>>>>>> 
>>>>>> Why don't prepare bio as same as wb.m_page? Won't that save more 
>>>>>> time
>>>>>> for ufshpb_issue_pre_req()?
>>>>> 
>>>>> It is pre_req pool. So although we prepare bio at this time, it just
>>>>> only for first pre_req.
>>>> 
>>>> I meant removing the bio_alloc() in ufshpb_issue_pre_req() and
>>>> bio_put()
>>>> in ufshpb_pre_req_compl_fn(). bios, in pre_req's case, just hold a
>>>> page.
>>>> So, prepare 16 (if queue depth is 32) bios here, just use them along
>>>> with
>>>> wb.m_page and call bio_reset() in ufshpb_pre_req_compl_fn(). Shall it
>>>> work?
>>>> 
>>> 
>>> If it works, you can even have the bio_add_pc_page() called here. 
>>> Later
>>> in
>>> ufshpb_execute_pre_req(), you don't need to call
>>> ufshpb_pre_req_add_bio_page(),
>>> just call ufshpb_prep_entry() once instead - it save many repeated 
>>> steps
>>> for a
>>> pre_req, and you don't even need to call bio_reset() in this case, 
>>> since
>>> for a
>>> bio, nothing changes after it is binded with a specific page...
>> 
>> Hi, Can Guo
>> 
>> I tried the idea that you suggested, but it doesn't work properly.
>> This optimization should be done next time for enhancement.
> 
>Can you elaborate please? Any error seen?
> 
>Per my understanding, in the case for pre_reqs, a bio is no different
>from a page. Here it can reserve 16 pages for later use, which can be
>done the same for bios.

I found some problem with re-using pre allocated bio.

The following kernel message is related with problem.
[    2.750530] ------------[ cut here ]------------
[    2.751404] WARNING: CPU: 4 PID: 170 at drivers/scsi/scsi_lib.c:1020 scsi_alloc_sgtables+0x253/0x2b0
[    2.753054] Modules linked in:
[    2.753651] CPU: 4 PID: 170 Comm: mount Not tainted 5.12.0-rc1+ #331
[    2.754752] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
[    2.756813] RIP: 0010:scsi_alloc_sgtables+0x253/0x2b0
[    2.757699] Code: 85 c0 74 19 41 0f b6 44 24 18 8d 50 e0 83 fa 03 76 30 41 bd 01 00 00 00 e9 1f fe ff ff be 01 00 00 00 45 31 ed e9 19 fe ff ff <0f> 0b b8 0a f
[    2.761021] RSP: 0018:ffffb06e0027f538 EFLAGS: 00010246
[    2.761902] RAX: 0000000000000000 RBX: ffff9c3a42d424d0 RCX: ffffb06e0027f5e0
[    2.763184] RDX: ffff9c3a42d426a8 RSI: 0000000000000000 RDI: ffff9c3a42d424d0
[    2.764446] RBP: ffffb06e0027f570 R08: 0000000000000000 R09: 0000000000000000
[    2.765704] R10: ffffffff8eb0dda0 R11: 00000000fffb7675 R12: ffff9c3a42d423c0
[    2.766976] R13: 0000000000000000 R14: ffff9c3a41bed000 R15: ffff9c3a420f4000
[    2.768225] FS:  00007f42d1eab100(0000) GS:ffff9c3b77c00000(0000) knlGS:0000000000000000
[    2.769666] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    2.770719] CR2: 00007f42d1ac1000 CR3: 0000000104bee006 CR4: 0000000000370ee0
[    2.771997] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[    2.773288] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[    2.774543] Call Trace:
[    2.775092]  scsi_queue_rq+0x9b6/0xb20
[    2.775754]  __blk_mq_try_issue_directly+0x150/0x1f0
[    2.776636]  blk_mq_request_issue_directly+0x49/0x80
[    2.777616]  blk_insert_cloned_request+0x85/0xd0
[    2.778470]  ufshpb_prep.cold+0x793/0x7be
[    2.779179]  ufshcd_queuecommand+0x114/0x690
[    2.779986]  scsi_queue_rq+0x38a/0xb20
[    2.780755]  blk_mq_dispatch_rq_list+0x13d/0x760
[    2.781605]  ? dd_dispatch_request+0x67/0x1c0
[    2.782337]  __blk_mq_do_dispatch_sched+0xb5/0x2c0
[    2.783291]  __blk_mq_sched_dispatch_requests+0x13c/0x180
[    2.784209]  blk_mq_sched_dispatch_requests+0x30/0x60
[    2.785195]  __blk_mq_run_hw_queue+0x49/0x90
[    2.786024]  __blk_mq_delay_run_hw_queue+0x162/0x180
[    2.786890]  blk_mq_run_hw_queue+0x85/0xe0
[    2.787590]  blk_mq_sched_insert_requests+0xdf/0x2b0
[    2.788558]  blk_mq_flush_plug_list+0x118/0x240
[    2.789405]  blk_flush_plug_list+0xde/0x110
[    2.790225]  blk_finish_plug+0x21/0x30
[    2.790878]  read_pages+0x16a/0x1d0
[    2.791534]  page_cache_ra_unbounded+0x123/0x1c0
[    2.792392]  do_page_cache_ra+0x38/0x40
[    2.793183]  force_page_cache_ra+0x97/0x110
[    2.793875]  page_cache_sync_ra+0x26/0x50
[    2.794671]  filemap_get_pages+0xc8/0x4b0
[    2.795482]  filemap_read+0xc9/0x340
[    2.796144]  ? find_held_lock+0x31/0x90
[    2.796809]  generic_file_read_iter+0xcc/0x130
[    2.797644]  blkdev_read_iter+0x30/0x40
[    2.798436]  new_sync_read+0x10e/0x190
[    2.799112]  vfs_read+0x178/0x1d0
[    2.799732]  ksys_read+0x6b/0xf0
[    2.800361]  __x64_sys_read+0x15/0x20
[    2.801027]  do_syscall_64+0x38/0x50
[    2.801770]  entry_SYSCALL_64_after_hwframe+0x44/0xae
[    2.802655] RIP: 0033:0x7f42d209a461
[    2.803313] Code: fe ff ff 50 48 8d 3d fe d0 09 00 e8 e9 03 02 00 66 0f 1f 84 00 00 00 00 00 48 8d 05 99 62 0d 00 8b 00 85 c0 75 13 31 c0 0f 05 <48> 3d 00 f0 8
[    2.806632] RSP: 002b:00007ffe7b88bc88 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
[    2.807942] RAX: ffffffffffffffda RBX: 000055ccb2e070d0 RCX: 00007f42d209a461
[    2.809218] RDX: 0000000000040000 RSI: 00007f42d1ac1038 RDI: 0000000000000004
[    2.810482] RBP: 000055ccb2e07120 R08: 00007f42d1ac1010 R09: 0000000000000000
[    2.811729] R10: 0000000000000022 R11: 0000000000000246 R12: 0000003b95fc0000
[    2.813005] R13: 0000000000040000 R14: 00007f42d1ac1028 R15: 00007f42d1ac1010
[    2.814276] irq event stamp: 9319
[    2.814868] hardirqs last  enabled at (9327): [<ffffffff8c4d2033>] console_unlock+0x4d3/0x5e0
[    2.816349] hardirqs last disabled at (9336): [<ffffffff8c4d1fa6>] console_unlock+0x446/0x5e0
[    2.817837] softirqs last  enabled at (8674): [<ffffffff8d4002ec>] __do_softirq+0x2ec/0x40f
[    2.819298] softirqs last disabled at (8669): [<ffffffff8c46ad9e>] irq_exit_rcu+0xae/0xb0
[    2.820744] ---[ end trace af3986a7787eeecf ]---

It is related to bi_iter value of bio is changed after use it.

Thanks,
Daejun

>This is not an enhancement, but a doubt - why not? Unless it is not 
>doable.
> 
>Thanks,
>Can Guo.
> 
>> 
>> Thanks
>> Daejun
>> 
>>> Can Guo.
>>> 
>>>> Thanks,
>>>> Can Guo.
>>>> 
>>>>> After use it, it should be prepared bio at issue phase.
>>>>> 
>>>>> Thanks,
>>>>> Daejun
>>>>> 
>>>>>> 
>>>>>> Thanks,
>>>>>> Can Guo.
>>>>>> 
>>>>>>> +
>>>>>>> +                pre_req->wb.m_page = alloc_page(GFP_KERNEL |
>>>>>>> __GFP_ZERO);
>>>>>>> +                if (!pre_req->wb.m_page) {
>>>>>>> +                        for (j = 0; j < i; j++)
>>>>>>> +
>>>>>>> __free_page(hpb->pre_req[j].wb.m_page);
>>>>>>> +
>>>>>>> +                        goto release_mem;
>>>>>>> +                }
>>>>>>> +                list_add_tail(&pre_req->list_req,
>>>>>>> &hpb->lh_pre_req_free);
>>>>>>> +        }
>>>>>>> +
>>>>>>> +        return 0;
>>>>>>> +release_mem:
>>>>>>> +        kfree(hpb->pre_req);
>>>>>>> +        return -ENOMEM;
>>>>>>> +}
>>>>>>> +
>>>>>> 
>>>>>> 
>>>>>> 
>>> 
>>> 
>>> 
> 
> 
>