Bug 1613425

I don't see details on hardware config, tuned profile or vdo thread config used in your test. Having that info associated with the BZ will be helpful.

I cloned this bug, so adding needinfo on the original reporter

tuned profile -> virtual-host

vdo options -> 
blockmapcachesize=128M
readcache=enabled
readcachesize=20M
emulate512=on
writepolicy=auto
slabsize=32G
Threads are not reconfigured, they are with default with default count what VDO sets.

Hardware: 
Attaching dmidecode output for that.

Created attachment 1474880 [details]
Smerf_Machine_dmidecode

Please let me know if any other info needed.

Small Correction in the FIO Command provided in the description. The throughput difference was obtained in FIO Sequential Write. This command with the correction is this one:

 fio --name=writetest --ioengine=sync --rw=write --direct=0 --create_on_open=1 --fsync_on_close=1 --bs=128k --directory=<test-dir-gluster> --filename_format=f.\$jobnum.\$filenum --filesize=16g --size=16g --numjobs=4

Are there any tunables to reduce the performance impact we're seeing?
Do you have test results with 4K block writes? Do you see the same drop?
Do you see a drop with a non-gluster setup for similar test?

Since we don't know where the bottleneck is coming from it is difficult to say if VOD tunables will help increase performance.  Do you know if there was an increase in aggregate performance when running this test on multiple VMs?  If so, then the layers above VDO might not be filling VDO's queues. 

It is recommended to do a full suite of performance test on each layer of the stack, tuning along the way, to find the best performance.  If not having enough threads in VDO is the issue, then you might see better performance by increasing the logical and physical threads to 2 or 4.

We can do some test runs using this fio command on our non-gluster systems and provide results.  Can you provide details as to why this fio command is interesting?  What type of workload
is it simulating?

Ran some tests on a Samsung 850 Pro to compare the performance of VDO vs. baseline using the fio command listed above.  The setup does not have Gluster involved or virtual machine, but was run directly on hardware.  Here is the setup:

1. vdo create --name=vdo1 --device=$drive --emulate512=enabled  
2. mkfs.xfs -K -i size=512 -n size=8192 <block device> -f
3. fio --name=write --ioengine=sync --rw=write --direct=0 --create_on_open=1 --fsync_on_close=1 --bs=128k --directory=<dir> --filesize=10g --size=10g --numjobs=4

Here are the results
basline test name <test|size|jobs|device name>
vdo test name <test|size|jobs|physical threads|logical threads|device name>

Test	                MB/s    % diff	
baseline-10-4-dm-2	697	--
vdo-10-4-1-1-dm-2	545	21.81%

Results when increasing the logical and physical threads

vdo-10-4-1-2-dm-2	539	22.67%
vdo-10-4-1-4-dm-2	516	25.97%
vdo-10-4-2-1-dm-2	563	19.23%
vdo-10-4-2-2-dm-2	550	21.09%
vdo-10-4-2-4-dm-2	529	24.10%
vdo-10-4-4-1-dm-2	540	22.53%
vdo-10-4-4-2-dm-2	533	23.53%
vdo-10-4-4-4-dm-2	540	22.53%

I'm not seeing the large performance hit as this level.  I'll stand up a VM to see how it 
performs on top of baseline and VDO.  Could someone verify that the filesystem configuration is 
correct?

For another perspective, running the test you provided on a laptop with a single Samsung SSD and two cores I see:

320 MB/s without VDO
166 MB/s with VDO

That's with the virtual-host tuned profile.  I'm pretty sure I'll never get the throughput that Dennis is seeing because my laptop only has two physical cores.  My experience is that a physical core can process somewhere between 30K and 50K 4K blcks per second, which translates to 156 MB/s which is right in the range I'm seeing.

I would like to see the full config+stats output for VDO and the logs.

1. Can you paste the output of vdo status?
2. Also, can you attach /var/log/messages?

Thank you.

Thanks, Sahina.

I was looking for the VDO write policy configurations, which can change depending on the media used.  While bug 1565467 has the system configuration I didn't see
how VDO was configured with both SSD and HDD.  This could be important if one device was in sync mode and the other was in async mode.

# egrep "write policy|REQ_F" | /var/log/messages
Apr  9 11:15:23 rhsqa-grafton8 kernel: kvdo0:dmsetup: starting device 'vdo_sdb' device instantiation 0 write policy auto
Apr  9 11:15:23 rhsqa-grafton8 kernel: kvdo0:dmsetup: underlying device, REQ_FLUSH: not supported, REQ_FUA: not supported

command vdo_status output:

VDO status:
  Date: '2018-04-10 11:42:08+05:30'
  Node: <host name removed>
Kernel module:
  Loaded: true
  Name: kvdo
  Version information:
    kvdo version: 6.1.0.153
Configuration:
  File: /etc/vdoconf.yml
  Last modified: '2018-04-09 11:15:25'
VDOs:
  vdo_sdb:
    Acknowledgement threads: 1
    Activate: enabled
    Bio rotation interval: 64
    Bio submission threads: 4
    Block map cache size: 128M
    Block map period: 16380
    Block size: 4096
    CPU-work threads: 2
    Compression: enabled
    Configured write policy: auto
    Deduplication: enabled
    Device mapper status: 0 419430400000 vdo /dev/sdb albserver online cpu=2,bio=4,ack=1,bioRotationInterval=64
    Emulate 512 byte: enabled
    Hash zone threads: 1
    Index checkpoint frequency: 0
    Index memory setting: 0.25
    Index parallel factor: 0
    Index sparse: disabled
    Index status: online
    Logical size: 200000G
    Logical threads: 1
    Physical size: 20979200M
    Physical threads: 1
    Read cache: enabled
    Read cache size: 20M
    Slab size: 32G
    Storage device: /dev/sdb
    VDO statistics:
      /dev/mapper/vdo_sdb:
        write policy: sync

Testing results


In testing VDO with a Samsung 850 the storage stack was configured with VDO, XFS,
and then a RHEL 7.5 VM.  
[VM]
1. FIO was installed on the VM
2. a default virtio block device was created on the VDO storage device (Samsung 850)
3. virtio block device was formatted "mkfs.xfs -K -i size=512 -n size=8192 <block device> -f"
4. fio --name=write --ioengine=sync --rw=write --direct=0 --create_on_open=1 --fsync_on_close=1 --bs=128k --directory=<dir> --filesize=10g --size=10g --numjobs=4

Software stack
[VM] RHEL 7.5 server - virtio 100G block device qcow2
[XFS] mkfs.xfs -K -i size=512 -n size=8192 <block device> -f
[VDO] vdo create --name=vdo1 --device=$drive --emulate512=enabled

Here are the changes in tests
Read Cache	- Read cache was enabled with 20MB
No Read Cache	- Read cache was disabled
L+P = 2	vm-vdo  - VDO's threads were increased from 1 to 2 for logical and physical threads
VM Cores 1 -> 4 - VM's cores were increased from 1 to 4
async -> sync   - VD0's write policy was changed from async -> sync ( the default is auto, so if the device supports flush or fua or both then VDO will set the device to async.  If the device doesn't support flush or fua VDO will be set to sync.


Results:

Test               MB/s    % diff
VM's Baseline      507                   
Read Cache	   347	   31.56%  (this is closest to the RHHI config, though without Gluster)
No Read Cache	   348	   31.36%
L+P = 2	vm-vdo	   371	   26.82%
VM Cores 1 -> 4	   351	   30.77%
async -> sync	   151	   70.22%  (This result is interesting and the reason why I'm interested in knowing how the devices are configured regarding VDO's write policy)

Looking at the difference between tests:

Test description: 
baseline-10-4-dm-2  - baseline test result from comment 10
VM's Baseline       - baseline result from with in a VM reported in this comment
Read Cache          - VDO test result from within a VM when the backing storage is VDO reported in this comment
vdo-10-4-1-1-dm-2   - VDO test result from comment 10 

Comparing baseline-10-4-dm-2 (referred to as baseline below) to he other results we see:

Test                    MB/s    % diff
baseline-10-4-dm-2	697	
VM's Baseline	        507	27.26%
vdo-10-4-1-1-dm-2	545	21.81%
Read Cache	        347	50.22%

- A 21.81% performance drop was seen when comparing baseline to VDO
- A 27.26% performance drop was seen when comparing baseline to baseline within a VM
- A 50.22% performance drop was seen when comparing baseline to VM volume backed by VDO
        - however, this is a 36.33% performance drop from VDO's performance outside of a VM (vdo-10-4-1-1-dm-2)
        - and 31.56% performance drop from VM's Baseline from within the VM

Current path of investigating performance is:

1. Understand whether write policy is impacting performance (effected by flushes or FUA)
   - Testing from the RHHI team will be needed to identify whether changing the write policy improves performance
2. Is sub 4K writes impacting performance?  Louis has some questions out to the XFS team.
3. Some gains have been seen by increasing VDO's threads in the 1 VM case (4%), while this isn't much, when 
   using multiple VM the increases should be greater. 
   - RHHI team will have to test performance when increasing VDO threads

Regarding the questions about sub-4k IO, if xfs's mkfs-time sector size is 512, it will do metadata IOs (at least to the log) in 512-byte units.

What does:

# lsblk -t </dev/vdo-device>

say about the device topology?

Also, what does xfs_info say about the slow xfs filesystem in question?

Raising needinfo on the original reporter

(In reply to Dennis Keefe from comment #15)
> Current path of investigating performance is:
> 
> 1. Understand whether write policy is impacting performance (effected by
> flushes or FUA)
>    - Testing from the RHHI team will be needed to identify whether changing
> the write policy improves performance

Currently it is auto and it should be set to sync/async ?

> 2. Is sub 4K writes impacting performance?  Louis has some questions out to
> the XFS team.
> 3. Some gains have been seen by increasing VDO's threads in the 1 VM case
> (4%), while this isn't much, when 
>    using multiple VM the increases should be greater. 
>    - RHHI team will have to test performance when increasing VDO threads

What should be the increased thread_count ? Should set each thread to double ?

(In reply to Nikhil Chawla from comment #19)
> (In reply to Dennis Keefe from comment #15)
> > Current path of investigating performance is:
> > 
> > 1. Understand whether write policy is impacting performance (effected by
> > flushes or FUA)
> >    - Testing from the RHHI team will be needed to identify whether changing
> > the write policy improves performance
> 
> Currently it is auto and it should be set to sync/async ?
In comment 13 you can find how to find out what auto is configured to from logs or
you can use vdo status command and look for "write policy".  
My suggestion is that you should find out what this is configured for then 
run another test after switching modes to see if it helps with performance.  This can be done online by using the command "vdo changeWritePolicy --name=<volume name> --writePolicy=<sync|async>.

> 
> > 2. Is sub 4K writes impacting performance?  Louis has some questions out to
> > the XFS team.
> > 3. Some gains have been seen by increasing VDO's threads in the 1 VM case
> > (4%), while this isn't much, when 
> >    using multiple VM the increases should be greater. 
> >    - RHHI team will have to test performance when increasing VDO threads
> 
> What should be the increased thread_count ? Should set each thread to double
> ?
This can only be determined by running performance tests and scaling threads and VMs on the system configuration you expect to be used by customers.  A guess as to what might work for SSD and NVMe in RHHI would be 4 logical, 4 physical, 5 CPU.

Please let us know how those results work out for you.  The other advantage of a higher number of threads can be that they spread the load better and thus have less impact on other processes.  The downside is that if you have too many threads and not enough processor cores, it can actually slow you down.

from comment 19 can you tell me what the write policy mode is on the SSD configuration of VDO?

(In reply to Dennis Keefe from comment #22)
> from comment 19 can you tell me what the write policy mode is on the SSD
> configuration of VDO?

For all the devices, currently it is auto.

Nikhil,

When configured for auto VDO checks the device before creating the volume to determine whether to set the write policy to sync or async mode.  I would like to know what VDO selected for the test run with SSDs.  The output of vdo status will show what the write policy is set to.

Created attachment 1478031 [details]
vdo_status_ouput

Nikhil,

Have you tried the tuning suggested by Dennis above yet of increasing the thread counts for VDO to 4 logical, 4 physical, and 5 CPU? Looking at the SSD numbers, that would seem like the next logical step here. We all knew going in that hard drive will take a substantial hit on sequential IO so spending time on that doesn't make much sense, at least until you've fully explored the SSD case.  

I also notice you've set a readcache which is not something we do by default?  Have you checked to see if that is helping performance for your test cases?

Nikhil,
Thanks for the output of vdo status.  I see that the vdo volume was configured to sync by VDO.
The FIO command that you use generates compressible data (about 49%). You could also increase 
performance for this test case by changing the write policy to async.  

example of the fio test writing compressible data: 
# vdo create --name=vdo --device=/dev/dm-2
Creating VDO vdo
Starting VDO vdo
Starting compression on VDO vdo
VDO instance 14 volume is ready at /dev/mapper/vdo

# vdostats --hum
Device                    Size      Used Available Use% Space saving%
/dev/mapper/vdo         171.9G      4.0G    167.9G   2%           N/A

# mkfs.xfs -K /dev/mapper/vdo ;mount /dev/mapper/vdo /vdo1
meta-data=/dev/mapper/vdo        isize=512    agcount=4, agsize=10988974 blks
         =                       sectsz=4096  attr=2, projid32bit=1
         =                       crc=1        finobt=0, sparse=0
data     =                       bsize=4096   blocks=43955896, imaxpct=25
         =                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096   ascii-ci=0 ftype=1
log      =internal log           bsize=4096   blocks=21462, version=2
         =                       sectsz=4096  sunit=1 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0

# vdostats --hum
Device                    Size      Used Available Use% Space saving%
/dev/mapper/vdo         171.9G      4.0G    167.9G   2%           99%
# fio --name=write --ioengine=sync --rw=write --direct=0 --create_on_open=1 --fsync_on_close=1 --bs=128k --directory=/vdo1 --filesize=3g --size=3g --numjobs=4

# vdostats --hum
Device                    Size      Used Available Use% Space saving%
/dev/mapper/vdo         171.9G     10.1G    161.8G   5%           49%


If you do not want to write compressible data in this testing then add the --refill_buffers=1 option to the fio command

The space savings is 0 since the data is now unique and not compressible.

# fio --name=write --ioengine=sync --rw=write --direct=0 --create_on_open=1 --fsync_on_close=1 --bs=128k --directory=/vdo1 --filesize=3g --size=3g --numjobs=4 --refill_buffers=1

# vdostats --hum
Device                    Size      Used Available Use% Space saving%
/dev/mapper/vdo         171.9G     16.0G    155.9G   9%            0%

(In reply to Louis Imershein from comment #26)
> Nikhil,
> 
> Have you tried the tuning suggested by Dennis above yet of increasing the
> thread counts for VDO to 4 logical, 4 physical, and 5 CPU? Looking at the
> SSD numbers, that would seem like the next logical step here. We all knew
> going in that hard drive will take a substantial hit on sequential IO so
> spending time on that doesn't make much sense, at least until you've fully
> explored the SSD case.  

I've not tried the recently suggested tunings because I've not any set of machines right now. But in 2 weeks, I'll be getting my reservation most probably. 

> I also notice you've set a readcache which is not something we do by
> default?  Have you checked to see if that is helping performance for your
> test cases?
readcache comes enabled by default in RHHI. So, I'll add this also to the list of experiments.

(In reply to Dennis Keefe from comment #27)
> Nikhil,
> Thanks for the output of vdo status.  I see that the vdo volume was
> configured to sync by VDO.
> The FIO command that you use generates compressible data (about 49%). You
> could also increase 
> performance for this test case by changing the write policy to async.  
> 
> example of the fio test writing compressible data: 
> # vdo create --name=vdo --device=/dev/dm-2
> Creating VDO vdo
> Starting VDO vdo
> Starting compression on VDO vdo
> VDO instance 14 volume is ready at /dev/mapper/vdo
> 
> # vdostats --hum
> Device                    Size      Used Available Use% Space saving%
> /dev/mapper/vdo         171.9G      4.0G    167.9G   2%           N/A
> 
> # mkfs.xfs -K /dev/mapper/vdo ;mount /dev/mapper/vdo /vdo1
> meta-data=/dev/mapper/vdo        isize=512    agcount=4, agsize=10988974 blks
>          =                       sectsz=4096  attr=2, projid32bit=1
>          =                       crc=1        finobt=0, sparse=0
> data     =                       bsize=4096   blocks=43955896, imaxpct=25
>          =                       sunit=0      swidth=0 blks
> naming   =version 2              bsize=4096   ascii-ci=0 ftype=1
> log      =internal log           bsize=4096   blocks=21462, version=2
>          =                       sectsz=4096  sunit=1 blks, lazy-count=1
> realtime =none                   extsz=4096   blocks=0, rtextents=0
> 
> # vdostats --hum
> Device                    Size      Used Available Use% Space saving%
> /dev/mapper/vdo         171.9G      4.0G    167.9G   2%           99%
> # fio --name=write --ioengine=sync --rw=write --direct=0 --create_on_open=1
> --fsync_on_close=1 --bs=128k --directory=/vdo1 --filesize=3g --size=3g
> --numjobs=4
> 
> # vdostats --hum
> Device                    Size      Used Available Use% Space saving%
> /dev/mapper/vdo         171.9G     10.1G    161.8G   5%           49%
> 
> 
> If you do not want to write compressible data in this testing then add the
> --refill_buffers=1 option to the fio command
> 
> The space savings is 0 since the data is now unique and not compressible.
> 
> # fio --name=write --ioengine=sync --rw=write --direct=0 --create_on_open=1
> --fsync_on_close=1 --bs=128k --directory=/vdo1 --filesize=3g --size=3g
> --numjobs=4 --refill_buffers=1
> 
> # vdostats --hum
> Device                    Size      Used Available Use% Space saving%
> /dev/mapper/vdo         171.9G     16.0G    155.9G   9%            0%

Thanks for letting me know. I'll use this command for next round of runs.

From the initial bug description, step number 2.

2. Provision a vm and add (RAID6/SSD) storage disk to VM (Virtio-blk,thin-provisioned)

What is the disk configuration for the virtio-blk?  Is there an xml available for this VM?

(In reply to Dennis Keefe from comment #30)
> From the initial bug description, step number 2.
> 
> 2. Provision a vm and add (RAID6/SSD) storage disk to VM
> (Virtio-blk,thin-provisioned)
> 
> What is the disk configuration for the virtio-blk?  Is there an xml
> available for this VM?

I am attaching the VM xml file in the bz, you can check for "vda", that is a "virtio-blk" device in a VM created over one of my setup.

Created attachment 1481322 [details]
VM_sample.xml

Thanks.  What is the size of "vda"?

(In reply to Dennis Keefe from comment #33)
> Thanks.  What is the size of "vda"?

Since, its an OS disk ,so usually I keep it 40-50GB .

Correct.  I think it is important to know whether there are performance changes 
when changing the write policy and or threads.

We know that VDO does not give significant performance in RHHI-V.Right now we are looking only high priority customer bugs fix and also we don't have plan now for VDO fixes.So closing this bug for now will reopen if any customer comes with same issue.