Re: [PATCH v4 01/11] block: make generic_make_request handle arbitrarily sized bios

From: Ming Lin
Date: Wed Jun 10 2015 - 18:06:26 EST

On Wed, Jun 10, 2015 at 2:46 PM, Mike Snitzer <snitzer@xxxxxxxxxx> wrote:
> On Wed, Jun 10 2015 at 5:20pm -0400,
> Ming Lin <mlin@xxxxxxxxxx> wrote:
>
>> On Mon, Jun 8, 2015 at 11:09 PM, Ming Lin <mlin@xxxxxxxxxx> wrote:
>> > On Thu, 2015-06-04 at 17:06 -0400, Mike Snitzer wrote:
>> >> We need to test on large HW raid setups like a Netapp filer (or even
>> >> local SAS drives connected via some SAS controller). Like a 8+2 drive
>> >> RAID6 or 8+1 RAID5 setup. Testing with MD raid on JBOD setups with 8
>> >> devices is also useful. It is larger RAID setups that will be more
>> >> sensitive to IO sizes being properly aligned on RAID stripe and/or chunk
>> >> size boundaries.
>> >
>> > Here are tests results of xfs/ext4/btrfs read/write on HW RAID6/MD RAID6/DM stripe target.
>> > Each case run 0.5 hour, so it took 36 hours to finish all the tests on 4.1-rc4 and 4.1-rc4-patched kernels.
>> >
>> > No performance regressions were introduced.
>> >
>> > Test server: Dell R730xd(2 sockets/48 logical cpus/264G memory)
>> > HW RAID6/MD RAID6/DM stripe target were configured with 10 HDDs, each 280G
>> > Stripe size 64k and 128k were tested.
>> >
>> > devs="/dev/sdb /dev/sdc /dev/sdd /dev/sde /dev/sdf /dev/sdg /dev/sdh /dev/sdi /dev/sdj /dev/sdk"
>> > spare_devs="/dev/sdl /dev/sdm"
>> > stripe_size=64 (or 128)
>> >
>> > MD RAID6 was created by:
>> > mdadm --create --verbose /dev/md0 --level=6 --raid-devices=10 $devs --spare-devices=2 $spare_devs -c $stripe_size
>> >
>> > DM stripe target was created by:
>> > pvcreate $devs
>> > vgcreate striped_vol_group $devs
>> > lvcreate -i10 -I${stripe_size} -L2T -nstriped_logical_volume striped_vol_group
>
> DM had a regression relative to merge_bvec that wasn't fixed until
> recently (it wasn't in 4.1-rc4), see commit 1c220c69ce0 ("dm: fix
> casting bug in dm_merge_bvec()"). It was introduced in 4.1.
>
> So your 4.1-rc4 DM stripe testing may have effectively been with
> merge_bvec disabled.

I'l rebase it to latest Linus tree and re-run DM stripe testing.

>
>> > Here is an example of fio script for stripe size 128k:
>> > [global]
>> > ioengine=libaio
>> > iodepth=64
>> > direct=1
>> > runtime=1800
>> > time_based
>> > group_reporting
>> > numjobs=48
>> > gtod_reduce=0
>> > norandommap
>> > write_iops_log=fs
>> >
>> > [job1]
>> > bs=1280K
>> > directory=/mnt
>> > size=5G
>> > rw=read
>> >
>> > All results here: http://minggr.net/pub/20150608/fio_results/
>> >
>> > Results summary:
>> >
>> > 1. HW RAID6: stripe size 64k
>> > 4.1-rc4 4.1-rc4-patched
>> > ------- ---------------
>> > (MB/s) (MB/s)
>> > xfs read: 821.23 812.20 -1.09%
>> > xfs write: 753.16 754.42 +0.16%
>> > ext4 read: 827.80 834.82 +0.84%
>> > ext4 write: 783.08 777.58 -0.70%
>> > btrfs read: 859.26 871.68 +1.44%
>> > btrfs write: 815.63 844.40 +3.52%
>> >
>> > 2. HW RAID6: stripe size 128k
>> > 4.1-rc4 4.1-rc4-patched
>> > ------- ---------------
>> > (MB/s) (MB/s)
>> > xfs read: 948.27 979.11 +3.25%
>> > xfs write: 820.78 819.94 -0.10%
>> > ext4 read: 978.35 997.92 +2.00%
>> > ext4 write: 853.51 847.97 -0.64%
>> > btrfs read: 1013.1 1015.6 +0.24%
>> > btrfs write: 854.43 850.42 -0.46%
>> >
>> > 3. MD RAID6: stripe size 64k
>> > 4.1-rc4 4.1-rc4-patched
>> > ------- ---------------
>> > (MB/s) (MB/s)
>> > xfs read: 847.34 869.43 +2.60%
>> > xfs write: 198.67 199.03 +0.18%
>> > ext4 read: 763.89 767.79 +0.51%
>> > ext4 write: 281.44 282.83 +0.49%
>> > btrfs read: 756.02 743.69 -1.63%
>> > btrfs write: 268.37 265.93 -0.90%
>> >
>> > 4. MD RAID6: stripe size 128k
>> > 4.1-rc4 4.1-rc4-patched
>> > ------- ---------------
>> > (MB/s) (MB/s)
>> > xfs read: 993.04 1014.1 +2.12%
>> > xfs write: 293.06 298.95 +2.00%
>> > ext4 read: 1019.6 1020.9 +0.12%
>> > ext4 write: 371.51 371.47 -0.01%
>> > btrfs read: 1000.4 1020.8 +2.03%
>> > btrfs write: 241.08 246.77 +2.36%
>> >
>> > 5. DM: stripe size 64k
>> > 4.1-rc4 4.1-rc4-patched
>> > ------- ---------------
>> > (MB/s) (MB/s)
>> > xfs read: 1084.4 1080.1 -0.39%
>> > xfs write: 1071.1 1063.4 -0.71%
>> > ext4 read: 991.54 1003.7 +1.22%
>> > ext4 write: 1069.7 1052.2 -1.63%
>> > btrfs read: 1076.1 1082.1 +0.55%
>> > btrfs write: 968.98 965.07 -0.40%
>> >
>> > 6. DM: stripe size 128k
>> > 4.1-rc4 4.1-rc4-patched
>> > ------- ---------------
>> > (MB/s) (MB/s)
>> > xfs read: 1020.4 1066.1 +4.47%
>> > xfs write: 1058.2 1066.6 +0.79%
>> > ext4 read: 990.72 988.19 -0.25%
>> > ext4 write: 1050.4 1070.2 +1.88%
>> > btrfs read: 1080.9 1074.7 -0.57%
>> > btrfs write: 975.10 972.76 -0.23%
>>
>> Hi Mike,
>>
>> How about these numbers?
>
> Looks fairly good. I just am not sure the workload is going to test the
> code paths in question like we'd hope. I'll have to set aside some time

How about adding some counters to record, for example, how many time
->merge_bvec is called in old kernel and how many time bio splitting is called
in patched kernel?

> to think through scenarios to test.

Great.

>
> My concern still remains that at some point it the future we'll regret
> not having merge_bvec but it'll be too late. That is just my own FUD at
> this point...
>
>> I'm also happy to run other fio jobs your team used.
>
> I've been busy getting DM changes for the 4.2 merge window finalized.
> As such I haven't connected with others on the team to discuss this
> issue.
>
> I'll see if we can make time in the next 2 days. But I also have
> RHEL-specific kernel deadlines I'm coming up against.
>
> Seems late to be staging this extensive a change for 4.2... are you
> pushing for this code to land in the 4.2 merge window? Or do we have
> time to work this further and target the 4.3 merge?

I'm OK to target the 4.3 merge.
But hope we can get it into linux-next tree ASAP for more wide tests.

>
> Mike
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