[GIT PULL] MD update for 4.9

[GIT PULL] MD update for 4.9

[Shaohua Li]

Hi Linus,
Please pull MD update for 4.9. This update includes:
- new AVX512 instruction based raid6 gen/recovery algorithm
- A couple of md-cluster related bug fixes
- Fix a potential deadlock
- Set nonrotational bit for raid array with SSD
- Set correct max_hw_sectors for raid5/6, which hopefuly can improve
  performance a little bit
- Other minor fixes

Thanks,
Shaohua

The following changes since commit 7d1e042314619115153a0f6f06e4552c09a50e13:

  Merge tag 'usercopy-v4.8-rc8' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux (2016-09-20 17:11:19 -0700)

are available in the git repository at:

  git://git.kernel.org/pub/scm/linux/kernel/git/shli/md.git tags/md/4.9-rc1

for you to fetch changes up to bb086a89a406b5d877ee616f1490fcc81f8e1b2b:

  md: set rotational bit (2016-10-03 10:20:27 -0700)

----------------------------------------------------------------
Chao Yu (1):
      raid5: fix to detect failure of register_shrinker

Gayatri Kammela (5):
      lib/raid6: Add AVX512 optimized gen_syndrome functions
      lib/raid6: Add AVX512 optimized recovery functions
      lib/raid6/test/Makefile: Add avx512 gen_syndrome and recovery functions
      lib/raid6: Add AVX512 optimized xor_syndrome functions
      raid6/test/test.c: bug fix: Specify aligned(alignment) attributes to the char arrays

Guoqing Jiang (9):
      md-cluster: call md_kick_rdev_from_array once ack failed
      md-cluster: use FORCEUNLOCK in lockres_free
      md-cluster: remove some unnecessary dlm_unlock_sync
      md: changes for MD_STILL_CLOSED flag
      md-cluster: clean related infos of cluster
      md-cluster: protect md_find_rdev_nr_rcu with rcu lock
      md-cluster: convert the completion to wait queue
      md-cluster: introduce dlm_lock_sync_interruptible to fix tasks hang
      md-cluster: make resync lock also could be interruptted

Shaohua Li (5):
      raid5: allow arbitrary max_hw_sectors
      md/bitmap: fix wrong cleanup
      md: fix a potential deadlock
      raid5: handle register_shrinker failure
      md: set rotational bit

 arch/x86/Makefile        |   5 +-
 drivers/md/bitmap.c      |   4 +-
 drivers/md/md-cluster.c  |  99 ++++++---
 drivers/md/md.c          |  44 +++-
 drivers/md/md.h          |   5 +-
 drivers/md/raid5.c       |  11 +-
 include/linux/raid/pq.h  |   4 +
 lib/raid6/Makefile       |   2 +-
 lib/raid6/algos.c        |  12 +
 lib/raid6/avx512.c       | 569 +++++++++++++++++++++++++++++++++++++++++++++++
 lib/raid6/recov_avx512.c | 388 ++++++++++++++++++++++++++++++++
 lib/raid6/test/Makefile  |   5 +-
 lib/raid6/test/test.c    |   7 +-
 lib/raid6/x86.h          |  10 +
 14 files changed, 1111 insertions(+), 54 deletions(-)
 create mode 100644 lib/raid6/avx512.c
 create mode 100644 lib/raid6/recov_avx512.c

Re: [GIT PULL] MD update for 4.9

[Doug Dumitru]

Mr. Li,

There is another thread in [linux-raid] discussing pre-fetches in the
raid-6 AVX2 code.  My testing implies that the prefetch distance is
too short.  In your new AVX512 code, it looks like there are 24
instructions, each with latencies of 1, between the prefetch and the
actual memory load.  I don't have a AVX512 CPU to try this on, but the
prefetch might do better at a bigger distance.  If I am not mistaken,
it takes a lot longer than 24 clocks to fetch 4 cache lines.

Just a comment while the code is still fluid.

Doug Dumitru
EasyCo LLC

On Thu, Oct 6, 2016 at 5:38 PM, Shaohua Li <shli@kernel.org> wrote:
> Hi Linus,
> Please pull MD update for 4.9. This update includes:
> - new AVX512 instruction based raid6 gen/recovery algorithm
> - A couple of md-cluster related bug fixes
> - Fix a potential deadlock
> - Set nonrotational bit for raid array with SSD
> - Set correct max_hw_sectors for raid5/6, which hopefuly can improve
>   performance a little bit
> - Other minor fixes
>
> Thanks,
> Shaohua
>
> The following changes since commit 7d1e042314619115153a0f6f06e4552c09a50e13:
>
>   Merge tag 'usercopy-v4.8-rc8' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux (2016-09-20 17:11:19 -0700)
>
> are available in the git repository at:
>
>   git://git.kernel.org/pub/scm/linux/kernel/git/shli/md.git tags/md/4.9-rc1
>
> for you to fetch changes up to bb086a89a406b5d877ee616f1490fcc81f8e1b2b:
>
>   md: set rotational bit (2016-10-03 10:20:27 -0700)
>
> ----------------------------------------------------------------
> Chao Yu (1):
>       raid5: fix to detect failure of register_shrinker
>
> Gayatri Kammela (5):
>       lib/raid6: Add AVX512 optimized gen_syndrome functions
>       lib/raid6: Add AVX512 optimized recovery functions
>       lib/raid6/test/Makefile: Add avx512 gen_syndrome and recovery functions
>       lib/raid6: Add AVX512 optimized xor_syndrome functions
>       raid6/test/test.c: bug fix: Specify aligned(alignment) attributes to the char arrays
>
> Guoqing Jiang (9):
>       md-cluster: call md_kick_rdev_from_array once ack failed
>       md-cluster: use FORCEUNLOCK in lockres_free
>       md-cluster: remove some unnecessary dlm_unlock_sync
>       md: changes for MD_STILL_CLOSED flag
>       md-cluster: clean related infos of cluster
>       md-cluster: protect md_find_rdev_nr_rcu with rcu lock
>       md-cluster: convert the completion to wait queue
>       md-cluster: introduce dlm_lock_sync_interruptible to fix tasks hang
>       md-cluster: make resync lock also could be interruptted
>
> Shaohua Li (5):
>       raid5: allow arbitrary max_hw_sectors
>       md/bitmap: fix wrong cleanup
>       md: fix a potential deadlock
>       raid5: handle register_shrinker failure
>       md: set rotational bit
>
>  arch/x86/Makefile        |   5 +-
>  drivers/md/bitmap.c      |   4 +-
>  drivers/md/md-cluster.c  |  99 ++++++---
>  drivers/md/md.c          |  44 +++-
>  drivers/md/md.h          |   5 +-
>  drivers/md/raid5.c       |  11 +-
>  include/linux/raid/pq.h  |   4 +
>  lib/raid6/Makefile       |   2 +-
>  lib/raid6/algos.c        |  12 +
>  lib/raid6/avx512.c       | 569 +++++++++++++++++++++++++++++++++++++++++++++++
>  lib/raid6/recov_avx512.c | 388 ++++++++++++++++++++++++++++++++
>  lib/raid6/test/Makefile  |   5 +-
>  lib/raid6/test/test.c    |   7 +-
>  lib/raid6/x86.h          |  10 +
>  14 files changed, 1111 insertions(+), 54 deletions(-)
>  create mode 100644 lib/raid6/avx512.c
>  create mode 100644 lib/raid6/recov_avx512.c
> --
> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html



-- 
Doug Dumitru
EasyCo LLC

Re: [GIT PULL] MD update for 4.9

[Linus Torvalds]

On Thu, Oct 6, 2016 at 10:39 PM, Doug Dumitru <doug@easyco.com> wrote:
>
> There is another thread in [linux-raid] discussing pre-fetches in the
> raid-6 AVX2 code.  My testing implies that the prefetch distance is
> too short.  In your new AVX512 code, it looks like there are 24
> instructions, each with latencies of 1, between the prefetch and the
> actual memory load.  I don't have a AVX512 CPU to try this on, but the
> prefetch might do better at a bigger distance.  If I am not mistaken,
> it takes a lot longer than 24 clocks to fetch 4 cache lines.

We have basically never had a case where prefetches were actually a good idea.

If the hardware doesn't do prefetching on its own (partly with just
physical memory patterns in the memory controller, partly just with
aggressive OoO), software isn't going to be able to improve on the
situation in general.

SW prefetching is a broken concept. You can make big differences for
very specific microarchitectures (usually the broken shit ones are the
ones that show it best), but in the general case it's pretty much
always a lost cause. We've had real cases where prefetching just then
made things worse on other hardware.

So just don't do it. It's benchmarketing for specific hardware, it's
not worth worrying about in the bigger picture. You'll find people
spend a lot of time tuning things for their particular hardware, and
it not helping at all on anything else.

Waste of time. Life is too short (and software is too complex) to try
to work around broken microarchitectures with sw prefetching.

              Linus

Re: [GIT PULL] MD update for 4.9

[Shaohua Li]

On Thu, Oct 06, 2016 at 10:39:21PM -0700, Doug Dumitru wrote:
> Mr. Li,
> 
> There is another thread in [linux-raid] discussing pre-fetches in the
> raid-6 AVX2 code.  My testing implies that the prefetch distance is
> too short.  In your new AVX512 code, it looks like there are 24
> instructions, each with latencies of 1, between the prefetch and the
> actual memory load.  I don't have a AVX512 CPU to try this on, but the
> prefetch might do better at a bigger distance.  If I am not mistaken,
> it takes a lot longer than 24 clocks to fetch 4 cache lines.
> 
> Just a comment while the code is still fluid.

I did try your patch and it improved 10% in my machine, but this isn't
relevent to the pull. We can do the tunning later if necessary. I'm
hoping the intel guys can share some hints, but apparently Linus isn't a
fan for such tuning.

Thanks,
Shaohua

> On Thu, Oct 6, 2016 at 5:38 PM, Shaohua Li <shli@kernel.org> wrote:
> > Hi Linus,
> > Please pull MD update for 4.9. This update includes:
> > - new AVX512 instruction based raid6 gen/recovery algorithm
> > - A couple of md-cluster related bug fixes
> > - Fix a potential deadlock
> > - Set nonrotational bit for raid array with SSD
> > - Set correct max_hw_sectors for raid5/6, which hopefuly can improve
> >   performance a little bit
> > - Other minor fixes
> >
> > Thanks,
> > Shaohua
> >
> > The following changes since commit 7d1e042314619115153a0f6f06e4552c09a50e13:
> >
> >   Merge tag 'usercopy-v4.8-rc8' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux (2016-09-20 17:11:19 -0700)
> >
> > are available in the git repository at:
> >
> >   git://git.kernel.org/pub/scm/linux/kernel/git/shli/md.git tags/md/4.9-rc1
> >
> > for you to fetch changes up to bb086a89a406b5d877ee616f1490fcc81f8e1b2b:
> >
> >   md: set rotational bit (2016-10-03 10:20:27 -0700)
> >
> > ----------------------------------------------------------------
> > Chao Yu (1):
> >       raid5: fix to detect failure of register_shrinker
> >
> > Gayatri Kammela (5):
> >       lib/raid6: Add AVX512 optimized gen_syndrome functions
> >       lib/raid6: Add AVX512 optimized recovery functions
> >       lib/raid6/test/Makefile: Add avx512 gen_syndrome and recovery functions
> >       lib/raid6: Add AVX512 optimized xor_syndrome functions
> >       raid6/test/test.c: bug fix: Specify aligned(alignment) attributes to the char arrays
> >
> > Guoqing Jiang (9):
> >       md-cluster: call md_kick_rdev_from_array once ack failed
> >       md-cluster: use FORCEUNLOCK in lockres_free
> >       md-cluster: remove some unnecessary dlm_unlock_sync
> >       md: changes for MD_STILL_CLOSED flag
> >       md-cluster: clean related infos of cluster
> >       md-cluster: protect md_find_rdev_nr_rcu with rcu lock
> >       md-cluster: convert the completion to wait queue
> >       md-cluster: introduce dlm_lock_sync_interruptible to fix tasks hang
> >       md-cluster: make resync lock also could be interruptted
> >
> > Shaohua Li (5):
> >       raid5: allow arbitrary max_hw_sectors
> >       md/bitmap: fix wrong cleanup
> >       md: fix a potential deadlock
> >       raid5: handle register_shrinker failure
> >       md: set rotational bit
> >
> >  arch/x86/Makefile        |   5 +-
> >  drivers/md/bitmap.c      |   4 +-
> >  drivers/md/md-cluster.c  |  99 ++++++---
> >  drivers/md/md.c          |  44 +++-
> >  drivers/md/md.h          |   5 +-
> >  drivers/md/raid5.c       |  11 +-
> >  include/linux/raid/pq.h  |   4 +
> >  lib/raid6/Makefile       |   2 +-
> >  lib/raid6/algos.c        |  12 +
> >  lib/raid6/avx512.c       | 569 +++++++++++++++++++++++++++++++++++++++++++++++
> >  lib/raid6/recov_avx512.c | 388 ++++++++++++++++++++++++++++++++
> >  lib/raid6/test/Makefile  |   5 +-
> >  lib/raid6/test/test.c    |   7 +-
> >  lib/raid6/x86.h          |  10 +
> >  14 files changed, 1111 insertions(+), 54 deletions(-)
> >  create mode 100644 lib/raid6/avx512.c
> >  create mode 100644 lib/raid6/recov_avx512.c
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 
> 
> 
> -- 
> Doug Dumitru
> EasyCo LLC

Re: [GIT PULL] MD update for 4.9

[Linus Torvalds]

On Fri, Oct 7, 2016 at 10:39 AM, Shaohua Li <shli@kernel.org> wrote:
>
> I did try your patch and it improved 10% in my machine, but this isn't
> relevent to the pull. We can do the tunning later if necessary. I'm
> hoping the intel guys can share some hints, but apparently Linus isn't a
> fan for such tuning.

We've had horrible experiences with prefetching in the past.  We've
seen microarchitectures that do really bad things when the prefetch
takes a TLB miss, for example, and suddenly they stall on the
prefetch, and actually slow the code down.

Admittedly, most of the bad cases are probably not a big deal for
streaming raid rebuild code, so it may well be that it works better
there.

So I'm not categorically against prefetching, but it needs to be
tested across a lot of different (micro-)architectures. Right now, I
guess something very specific like AVX512 means effectively just one
or two microarchitectures and then it's easy to say "it always helps".

The worst cases for the kernel have generally been in generic code.

                      Linus

Re: [GIT PULL] MD update for 4.9

[Doug Dumitru]

For the vast majority of cases, Linus is correct.  Pre-fetch is a
hardware specific tweak that just doesn't apply across the breadth of
systems Linus has to pay attention to.

In this case, our tunnel-vision is somewhat encouraged by the code and
logic at hand.  The AVX2 and AVX512 code is pretty specific to new,
64-bit, x86_64 platforms that tend to share a lot of cache behavior.
It is not like this will ever run on an Atom or ARM CPU.  Even more
important, the data access patterns are 100% defined by the task at
hand.  With RAID parity calculation, you are basically taking a stroll
through RAM with 100% defined patterns.  This is one case, where you
can pre-fetch memory enough ahead of time so that the hardware
prefetch unit never triggers and you will always be correct.

I am somewhat surprised you see 10%.  10% on an expensive function
like this is a lot.  Even more amazing is that the AVX2 and AVX512
code look to be memory bandwidth limited.  256 bytes of source reads
in about 30 clocks is about 17 GB/sec, which is faster than a single
RAM channel.  Congrats to Intel for "finding the next bottleneck".

I also see a follow-up from Linus, and again, totally agree with him.
I guess my take is that prefetch only works when you have a use case
where you are 100% correct with your pre-fetches.  I would also note
that this "raid case" is the default, clean array, parity calc code.
The same logic probably needs to be applied to the recovery cases, but
I have not looked at those yet.

Doug

On Fri, Oct 7, 2016 at 10:39 AM, Shaohua Li <shli@kernel.org> wrote:
> On Thu, Oct 06, 2016 at 10:39:21PM -0700, Doug Dumitru wrote:
>> Mr. Li,
>>
>> There is another thread in [linux-raid] discussing pre-fetches in the
>> raid-6 AVX2 code.  My testing implies that the prefetch distance is
>> too short.  In your new AVX512 code, it looks like there are 24
>> instructions, each with latencies of 1, between the prefetch and the
>> actual memory load.  I don't have a AVX512 CPU to try this on, but the
>> prefetch might do better at a bigger distance.  If I am not mistaken,
>> it takes a lot longer than 24 clocks to fetch 4 cache lines.
>>
>> Just a comment while the code is still fluid.
>
> I did try your patch and it improved 10% in my machine, but this isn't
> relevent to the pull. We can do the tunning later if necessary. I'm
> hoping the intel guys can share some hints, but apparently Linus isn't a
> fan for such tuning.
>
> Thanks,
> Shaohua
>
>> On Thu, Oct 6, 2016 at 5:38 PM, Shaohua Li <shli@kernel.org> wrote:
>> > Hi Linus,
>> > Please pull MD update for 4.9. This update includes:
>> > - new AVX512 instruction based raid6 gen/recovery algorithm
>> > - A couple of md-cluster related bug fixes
>> > - Fix a potential deadlock
>> > - Set nonrotational bit for raid array with SSD
>> > - Set correct max_hw_sectors for raid5/6, which hopefuly can improve
>> >   performance a little bit
>> > - Other minor fixes
>> >
>> > Thanks,
>> > Shaohua
>> >
>> > The following changes since commit 7d1e042314619115153a0f6f06e4552c09a50e13:
>> >
>> >   Merge tag 'usercopy-v4.8-rc8' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux (2016-09-20 17:11:19 -0700)
>> >
>> > are available in the git repository at:
>> >
>> >   git://git.kernel.org/pub/scm/linux/kernel/git/shli/md.git tags/md/4.9-rc1
>> >
>> > for you to fetch changes up to bb086a89a406b5d877ee616f1490fcc81f8e1b2b:
>> >
>> >   md: set rotational bit (2016-10-03 10:20:27 -0700)
>> >
>> > ----------------------------------------------------------------
>> > Chao Yu (1):
>> >       raid5: fix to detect failure of register_shrinker
>> >
>> > Gayatri Kammela (5):
>> >       lib/raid6: Add AVX512 optimized gen_syndrome functions
>> >       lib/raid6: Add AVX512 optimized recovery functions
>> >       lib/raid6/test/Makefile: Add avx512 gen_syndrome and recovery functions
>> >       lib/raid6: Add AVX512 optimized xor_syndrome functions
>> >       raid6/test/test.c: bug fix: Specify aligned(alignment) attributes to the char arrays
>> >
>> > Guoqing Jiang (9):
>> >       md-cluster: call md_kick_rdev_from_array once ack failed
>> >       md-cluster: use FORCEUNLOCK in lockres_free
>> >       md-cluster: remove some unnecessary dlm_unlock_sync
>> >       md: changes for MD_STILL_CLOSED flag
>> >       md-cluster: clean related infos of cluster
>> >       md-cluster: protect md_find_rdev_nr_rcu with rcu lock
>> >       md-cluster: convert the completion to wait queue
>> >       md-cluster: introduce dlm_lock_sync_interruptible to fix tasks hang
>> >       md-cluster: make resync lock also could be interruptted
>> >
>> > Shaohua Li (5):
>> >       raid5: allow arbitrary max_hw_sectors
>> >       md/bitmap: fix wrong cleanup
>> >       md: fix a potential deadlock
>> >       raid5: handle register_shrinker failure
>> >       md: set rotational bit
>> >
>> >  arch/x86/Makefile        |   5 +-
>> >  drivers/md/bitmap.c      |   4 +-
>> >  drivers/md/md-cluster.c  |  99 ++++++---
>> >  drivers/md/md.c          |  44 +++-
>> >  drivers/md/md.h          |   5 +-
>> >  drivers/md/raid5.c       |  11 +-
>> >  include/linux/raid/pq.h  |   4 +
>> >  lib/raid6/Makefile       |   2 +-
>> >  lib/raid6/algos.c        |  12 +
>> >  lib/raid6/avx512.c       | 569 +++++++++++++++++++++++++++++++++++++++++++++++
>> >  lib/raid6/recov_avx512.c | 388 ++++++++++++++++++++++++++++++++
>> >  lib/raid6/test/Makefile  |   5 +-
>> >  lib/raid6/test/test.c    |   7 +-
>> >  lib/raid6/x86.h          |  10 +
>> >  14 files changed, 1111 insertions(+), 54 deletions(-)
>> >  create mode 100644 lib/raid6/avx512.c
>> >  create mode 100644 lib/raid6/recov_avx512.c
>> > --
>> > To unsubscribe from this list: send the line "unsubscribe linux-raid" in
>> > the body of a message to majordomo@vger.kernel.org
>> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
>>
>>
>> --
>> Doug Dumitru
>> EasyCo LLC



-- 
Doug Dumitru
EasyCo LLC