[DRBD-user] [PATCH v4 01/11] block: make generic_make_request handle arbitrarily sized bios

Ming Lin mlin at kernel.org
Thu Jun 11 00:06:05 CEST 2015

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.


On Wed, Jun 10, 2015 at 2:46 PM, Mike Snitzer <snitzer at redhat.com> wrote:
> On Wed, Jun 10 2015 at  5:20pm -0400,
> Ming Lin <mlin at kernel.org> wrote:
>
>> On Mon, Jun 8, 2015 at 11:09 PM, Ming Lin <mlin at kernel.org> 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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