I've tried both deadline and noop schedulers. They both seem to
improve the behavior somewhat, in the sense that I no longer see the
panic-inducing two-minute hung tasks. But the interactive response
can remain poor, with the UI freezing for many seconds, including the
mouse cursor. The write bandwidth also goes down, from 8-10 MB/s to
2-4 MB/s, but I am not sure that's a concern because of the nature of
the test.
Interestingly, some of the very long blockages with the CFQ scheduler
happen on page faults from reading an mmapped file, as below.
In any case I appreciate all the help. This request was mostly to
make sure that I am not missing some major change to the I/O scheduler
("oh yes, there was this nasty bug, but it's fixed in 4.x..."). Maybe
this is not the right group though?
Thanks!
[215549.914848] INFO: task update_engine:1249 blocked for more than 120 seconds.
[215549.914858] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
disables this message.
[215549.914865] update_engine D ffff88017425ddb8 0 1249 1 0x00000000
[215549.914875] ffff88015558d710 0000000000000082 ffff8801780c5280
ffff88015558dfd8
[215549.914887] ffff88015558dfd8 0000000000011cc0 ffff88017425da00
ffff88017ca91cc0
[215549.914898] ffff88017cdc3b18 ffff88015558d7b8 ffffffff84d12ca5
0000000000000002
[215549.914909] Call Trace:
[215549.914920] [<ffffffff84d12ca5>] ? generic_block_bmap+0x65/0x65
[215549.914929] [<ffffffff850bf38b>] schedule+0x64/0x66
[215549.914935] [<ffffffff850bf509>] io_schedule+0x57/0x71
[215549.914942] [<ffffffff84d12cb3>] sleep_on_buffer+0xe/0x12
[215549.914951] [<ffffffff850bd8d3>] __wait_on_bit+0x46/0x76
[215549.914958] [<ffffffff850bd984>] out_of_line_wait_on_bit+0x81/0xa0
[215549.914966] [<ffffffff84d12ca5>] ? generic_block_bmap+0x65/0x65
[215549.914974] [<ffffffff84c51999>] ? autoremove_wake_function+0x34/0x34
[215549.914981] [<ffffffff84d13777>] __wait_on_buffer+0x26/0x28
[215549.914988] [<ffffffff84d13872>] wait_on_buffer+0x1e/0x20
[215549.914994] [<ffffffff84d1460a>] bh_submit_read+0x49/0x5b
[215549.915004] [<ffffffff84d7ea00>] ext4_get_branch+0x94/0x117
[215549.915011] [<ffffffff84d7eb72>] ext4_ind_map_blocks+0xef/0x513
[215549.915019] [<ffffffff84d4b7bb>] ext4_map_blocks+0x68/0x22a
[215549.915026] [<ffffffff84d4d724>] _ext4_get_block+0xd6/0x171
[215549.915034] [<ffffffff84d4d7d5>] ext4_get_block+0x16/0x18
[215549.915041] [<ffffffff84d1ba95>] do_mpage_readpage+0x1b1/0x50c
[215549.915048] [<ffffffff84d4d7bf>] ? _ext4_get_block+0x171/0x171
[215549.915057] [<ffffffff84cbfeef>] ? __lru_cache_add+0x39/0x75
[215549.915064] [<ffffffff84d4d7bf>] ? _ext4_get_block+0x171/0x171
[215549.915071] [<ffffffff84d1bee2>] mpage_readpages+0xf2/0x149
[215549.915078] [<ffffffff84d4d7bf>] ? _ext4_get_block+0x171/0x171
[215549.915085] [<ffffffff84d49ed5>] ext4_readpages+0x3c/0x43
[215549.915092] [<ffffffff84cbee01>] __do_page_cache_readahead+0x14d/0x203
[215549.915100] [<ffffffff84cbf0d1>] ra_submit+0x21/0x25
[215549.915107] [<ffffffff84cb7745>] filemap_fault+0x197/0x381
[215549.915115] [<ffffffff84cd14d0>] __do_fault+0xb0/0x34a
[215549.915122] [<ffffffff84cf9c30>] ? poll_select_copy_remaining+0x11d/0x11d
[215549.915130] [<ffffffff84cd3320>] handle_pte_fault+0x124/0x4f9
[215549.915137] [<ffffffff84cd446e>] handle_mm_fault+0x97/0xbb
[215549.915145] [<ffffffff84c297cd>] __do_page_fault+0x1d4/0x38c
[215549.915152] [<ffffffff84d23059>] ? eventfd_ctx_read+0x184/0x1aa
[215549.915159] [<ffffffff84c5f37a>] ? wake_up_state+0x12/0x12
[215549.915168] [<ffffffff84c39318>] ? timespec_add_safe+0x38/0x7b
[215549.915174] [<ffffffff84c299b7>] do_page_fault+0xe/0x10
[215549.915182] [<ffffffff850c05b2>] page_fault+0x22/0x30
On Thu, Jun 25, 2015 at 6:43 PM, Luigi Semenzato <semenzato@xxxxxxxxxx> wrote:
> I will try and report, thanks.
>
> On Thu, Jun 25, 2015 at 6:42 PM, Sergey Senozhatsky
> <sergey.senozhatsky.work@xxxxxxxxx> wrote:
>> On (06/25/15 18:31), Luigi Semenzato wrote:
>>> We're using CFQ.
>>>
>>> CONFIG_DEFAULT_IOSCHED="cfq"
>>> ...
>>> CONFIG_IOSCHED_CFQ=y
>>> CONFIG_IOSCHED_DEADLINE=y
>>> CONFIG_IOSCHED_NOOP=y
>>>
>>
>> any chance to try out DEADLINE?
>> CFQ, as far as I understand, doesn't make too much sense for SSDs.
>>
>> -ss
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