Re: strange observation, the queue depth is (64) meanwhile fw queue depth (65)

["Raphaël Bauduin" <rblists@gmail.com>]

On 03/28/2014 02:18 PM, Raphaël Bauduin wrote:
> On 03/27/2014 03:21 PM, Raphaël Bauduin wrote:
>> Hi,
>>
>> I have these messages logged on 2 different servers (one production, one
>> stand-by) when using recent vanilla kernels.
>>
>> I have found references to these logs, but this was supposedly
>> introduced in the 2.6.31 kernel.
>> However, running kernel 2.6.32.61, this message does not appear. It
>> appears when running kernel versions 3.12.15, 3.13.1 and 3.13.6. I
>> haven't tested other intermediate kernel versions.
>>
>> We had once the root filesystem remounted read-only on the production
>> server, and we found no significant error messages other than the one in
>> the subject of this mail. This makes me wary to ignore these messages,
>> and since then we went back to kernel 2.6.32.61.... I've tried running
>> kernels mentioned above on the stand-by server, and get the errors there
>> too.
>>
>> Here is the exact error message from dmesg:
>>
>> [ 3776.788033] sd 7:1:0:0: strange observation, the queue depth is (64)
>> meanwhile fw queue depth (65)
>>
>> and below are some other extracts from dmesg.
>>
>> Both servers have these errors on a RAID1 volume on which the root
>> partition is located.
>>
>> I hope someone can help me to resolve this. I can send any information
>> you might require.
>>
>> Thanks in advance
>>
>> Raphaël
>>
>>
>> [    2.978053] SCSI subsystem initialized
>> [    2.979969] Fusion MPT base driver 3.04.20
>> [    2.980059] Copyright (c) 1999-2008 LSI Corporation
>>
>>
>> [    3.712015] ioc0: LSISAS1064E B3: Capabilities={Initiator}
>>
>> [   16.516096] scsi7 : ioc0: LSISAS1064E B3, FwRev=01182b00h, Ports=1,
>> MaxQ=286, IRQ=16
>> [   16.536672] mptsas: ioc0: attaching ssp device: fw_channel 0, fw_id
>> 2, phy 0, sas_addr 0x500000e01ee1a602
>> [   16.538312] scsi 7:0:0:0: Direct-Access     FUJITSU  MBC2073RC  5201
>> PQ: 0 ANSI: 5
>> [   16.542605] mptsas: ioc0: attaching ssp device: fw_channel 0, fw_id
>> 1, phy 1, sas_addr 0x500000e01edab602
>> [   16.544158] scsi 7:0:1:0: Direct-Access     FUJITSU  MBC2073RC  5201
>> PQ: 0 ANSI: 5
>> [   16.548445] mptsas: ioc0: attaching raid volume, channel 1, id 0
>> [   16.549304] scsi 7:1:0:0: Direct-Access     LSILOGIC Logical Volume
>>   3000 PQ: 0 ANSI: 2
>> [   16.556492] sd 7:1:0:0: [sdr] 140623872 512-byte logical blocks:
>> (71.9 GB/67.0 GiB)
>> [   16.556824] sd 7:1:0:0: [sdr] Write Protect is off
>> [   16.556895] sd 7:1:0:0: [sdr] Mode Sense: 03 00 00 08
>> [   16.557109] sd 7:1:0:0: [sdr] No Caching mode page found
>> [   16.557180] sd 7:1:0:0: [sdr] Assuming drive cache: write through
>> [   16.558258] sd 7:1:0:0: [sdr] No Caching mode page found
>> [   16.558329] sd 7:1:0:0: [sdr] Assuming drive cache: write through
>> [   16.575039]  sdr: sdr1 sdr2
>> [   16.576018] sd 7:1:0:0: [sdr] No Caching mode page found
>> [   16.576088] sd 7:1:0:0: [sdr] Assuming drive cache: write through
>> [   16.576356] sd 7:1:0:0: [sdr] Attached SCSI disk
>>
>
>
> I have looked at the source code and the function
> mptsas_handle_queue_full_event is present and similar in all kernel
> versions I have tested, yet only version 2.6.32.61 doesn't log any error.
>
> I conclude that there's something else making that the queue is full.
> If this mailing list is not the right place to get help about this,
> please redirect me as I'm currently stuck on the 2.6.32 kernel due to
> this. Any help will be appreciated!
>
> Raphaël
>

I have found out that using the deadline scheduler on the disk causes 
the same error messages to appear, even with the 2.6.32 kernel. This 
does not happen with the cfq scheduler. I will try to increase the value 
in /sys/block/sdm/device/queue_depth (which is 64 like reported by the 
error message) and the value in /sys/block/sdm/queue/nr_requests 
accordingly (I read the cfq scheduler advises to use double the value 
for nr_requests).

I'll post further findings here, in case it can help someone

Raph




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