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

[Ming Lin <mlin@kernel.org>]

On Sun, May 31, 2015 at 11:02 PM, Ming Lin <mlin@kernel.org> wrote:
> On Thu, 2015-05-28 at 01:36 +0100, Alasdair G Kergon wrote:
>> On Wed, May 27, 2015 at 04:42:44PM -0700, Ming Lin wrote:
>> > Here are fio results of XFS on a DM stripped target with 2 SSDs + 1 HDD.
>> > Does it make sense?
>>
>> To stripe across devices with different characteristics?
>>
>> Some suggestions.
>>
>> Prepare 3 kernels.
>>   O - Old kernel.
>>   M - Old kernel with merge_bvec_fn disabled.
>>   N - New kernel.
>>
>> You're trying to search for counter-examples to the hypothesis that
>> "Kernel N always outperforms Kernel O".  Then if you find any, trying
>> to show either that the performance impediment is small enough that
>> it doesn't matter or that the cases are sufficiently rare or obscure
>> that they may be ignored because of the greater benefits of N in much more
>> common cases.
>>
>> (1) You're looking to set up configurations where kernel O performs noticeably
>> better than M.  Then you're comparing the performance of O and N in those
>> situations.
>>
>> (2) You're looking at other sensible configurations where O and M have
>> similar performance, and comparing that with the performance of N.
>
> I didn't find case (1).
>
> But the important thing for this series is to simplify block layer
> based on immutable biovecs. I don't expect performance improvement.
>
> Here is the changes statistics.
>
> "68 files changed, 336 insertions(+), 1331 deletions(-)"
>
> I run below 3 test cases to make sure it didn't bring any regressions.
> Test environment: 2 NVMe drives on 2 sockets server.
> Each case run for 30 minutes.
>
> 2) btrfs radi0
>
> mkfs.btrfs -f -d raid0 /dev/nvme0n1 /dev/nvme1n1
> mount /dev/nvme0n1 /mnt
>
> Then run 8K read.
>
> [global]
> ioengine=libaio
> iodepth=64
> direct=1
> runtime=1800
> time_based
> group_reporting
> numjobs=4
> rw=read
>
> [job1]
> bs=8K
> directory=/mnt
> size=1G
>
> 2) ext4 on MD raid5
>
> mdadm --create /dev/md0 --level=5 --raid-devices=2 /dev/nvme0n1 /dev/nvme1n1
> mkfs.ext4 /dev/md0
> mount /dev/md0 /mnt
>
> fio script same as btrfs test
>
> 3) xfs on DM stripped target
>
> pvcreate /dev/nvme0n1 /dev/nvme1n1
> vgcreate striped_vol_group /dev/nvme0n1 /dev/nvme1n1
> lvcreate -i2 -I4 -L250G -nstriped_logical_volume striped_vol_group
> mkfs.xfs -f /dev/striped_vol_group/striped_logical_volume
> mount /dev/striped_vol_group/striped_logical_volume /mnt
>
> fio script same as btrfs test
>
> ------
>
> Results:
>
>         4.1-rc4         4.1-rc4-patched
> btrfs   1818.6MB/s      1874.1MB/s
> ext4    717307KB/s      714030KB/s
> xfs     1396.6MB/s      1398.6MB/s

Hi Alasdair & Mike,

Would you like these numbers?
I'd like to address your concerns to move forward.

Thanks.