Re: [PATCH v7 0/5] Update LZ4 compressor module

[Minchan Kim]

Hi Sven,

On Sun, Feb 12, 2017 at 12:16:17PM +0100, Sven Schmidt wrote:
> 
> 
> 
> On 02/10/2017 01:13 AM, Minchan Kim wrote:
> > Hello Sven,
> >
> > On Thu, Feb 09, 2017 at 11:56:17AM +0100, Sven Schmidt wrote:
> >> Hey Minchan,
> >>
> >> On Thu, Feb 09, 2017 at 08:31:21AM +0900, Minchan Kim wrote:
> >>> Hello Sven,
> >>>
> >>> On Sun, Feb 05, 2017 at 08:09:03PM +0100, Sven Schmidt wrote:
> >>>>
> >>>> This patchset is for updating the LZ4 compression module to a version based
> >>>> on LZ4 v1.7.3 allowing to use the fast compression algorithm aka LZ4 fast
> >>>> which provides an "acceleration" parameter as a tradeoff between
> >>>> high compression ratio and high compression speed.
> >>>>
> >>>> We want to use LZ4 fast in order to support compression in lustre
> >>>> and (mostly, based on that) investigate data reduction techniques in behalf of
> >>>> storage systems.
> >>>>
> >>>> Also, it will be useful for other users of LZ4 compression, as with LZ4 fast
> >>>> it is possible to enable applications to use fast and/or high compression
> >>>> depending on the usecase.
> >>>> For instance, ZRAM is offering a LZ4 backend and could benefit from an updated
> >>>> LZ4 in the kernel.
> >>>>
> >>>> LZ4 homepage: http://www.lz4.org/
> >>>> LZ4 source repository: https://github.com/lz4/lz4
> >>>> Source version: 1.7.3
> >>>>
> >>>> Benchmark (taken from [1], Core i5-4300U @1.9GHz):
> >>>> ----------------|--------------|----------------|----------
> >>>> Compressor      | Compression  | Decompression  | Ratio
> >>>> ----------------|--------------|----------------|----------
> >>>> memcpy          |  4200 MB/s   |  4200 MB/s     | 1.000
> >>>> LZ4 fast 50     |  1080 MB/s   |  2650 MB/s     | 1.375
> >>>> LZ4 fast 17     |   680 MB/s   |  2220 MB/s     | 1.607
> >>>> LZ4 fast 5      |   475 MB/s   |  1920 MB/s     | 1.886
> >>>> LZ4 default     |   385 MB/s   |  1850 MB/s     | 2.101
> >>>>
> >>>> [1] http://fastcompression.blogspot.de/2015/04/sampling-or-faster-lz4.html
> >>>>
> >>>> [PATCH 1/5] lib: Update LZ4 compressor module
> >>>> [PATCH 2/5] lib/decompress_unlz4: Change module to work with new LZ4 module version
> >>>> [PATCH 3/5] crypto: Change LZ4 modules to work with new LZ4 module version
> >>>> [PATCH 4/5] fs/pstore: fs/squashfs: Change usage of LZ4 to work with new LZ4 version
> >>>> [PATCH 5/5] lib/lz4: Remove back-compat wrappers
> >>>
> >>> Today, I did zram-lz4 performance test with fio in current mmotm and
> >>> found it makes regression about 20%.
> >>>
> >>> "lz4-update" means current mmots(git://git.cmpxchg.org/linux-mmots.git) so
> >>> applied your 5 patches. (But now sure current mmots has recent uptodate
> >>> patches)
> >>> "revert" means I reverted your 5 patches in current mmots.
> >>>
> >>>                      revert    lz4-update
> >>>
> >>>       seq-write       1547       1339      86.55%
> >>>      rand-write      22775      19381      85.10%
> >>>        seq-read       7035       5589      79.45%
> >>>       rand-read      78556      68479      87.17%
> >>>    mixed-seq(R)       1305       1066      81.69%
> >>>    mixed-seq(W)       1205        984      81.66%
> >>>   mixed-rand(R)      17421      14993      86.06%
> >>>   mixed-rand(W)      17391      14968      86.07%
> >>
> >> which parts of the output (as well as units) are these values exactly?
> >> I did not work with fio until now, so I think I might ask before misinterpreting my results.
> >
> > It is IOPS.
> >
> >>  
> >>> My fio description file
> >>>
> >>> [global]
> >>> bs=4k
> >>> ioengine=sync
> >>> size=100m
> >>> numjobs=1
> >>> group_reporting
> >>> buffer_compress_percentage=30
> >>> scramble_buffers=0
> >>> filename=/dev/zram0
> >>> loops=10
> >>> fsync_on_close=1
> >>>
> >>> [seq-write]
> >>> bs=64k
> >>> rw=write
> >>> stonewall
> >>>
> >>> [rand-write]
> >>> rw=randwrite
> >>> stonewall
> >>>
> >>> [seq-read]
> >>> bs=64k
> >>> rw=read
> >>> stonewall
> >>>
> >>> [rand-read]
> >>> rw=randread
> >>> stonewall
> >>>
> >>> [mixed-seq]
> >>> bs=64k
> >>> rw=rw
> >>> stonewall
> >>>
> >>> [mixed-rand]
> >>> rw=randrw
> >>> stonewall
> >>>
> >>
> >> Great, this makes it easy for me to reproduce your test.
> >
> > If you have trouble to reproduce, feel free to ask me. I'm happy to test it. :)
> >
> > Thanks!
> >
> 
> Hi Minchan,
> 
> I will send an updated patch as a reply to this E-Mail. Would be really grateful If you'd test it and provide feedback!
> The patch should be applied to the current mmots tree.
> 
> In fact, the updated LZ4 _is_ slower than the current one in kernel. But I was not able to reproduce such large regressions
> as you did. I now tried to define FORCE_INLINE as Eric suggested. I also inlined some functions which weren't in upstream LZ4,
> but are defined as macros in the current kernel LZ4. The approach to replace LZ4_ARCH64 with the function call _seemed_ to behave
> worse than the macro, so I withdrew the change.
> 
> The main difference is, that I replaced the read32/read16/write... etc. functions using memcpy with the other ones defined 
> in upstream LZ4 (which can be switched using a macro). 
> The comment of the author stated, that they're as fast as the memcpy variants (or faster), but not as portable
> (which does not matter since we're not dependent for multiple compilers).
> 
> In my tests, this version is mostly as fast as the current kernel LZ4.

With a patch you sent, I cannot see enhancement so I wanted to dig in and
found how I was really careless.

I have tested both test with CONFIG_KASAN. OMG. With disabling it, I don't
see any regression any more. So, I'm really really *sorry* about noise and
wasting your time. However, I am curious why KASAN makes such difference.

The reason I tested new updated lz4 is description says lz4 fast and
want to use it in zram. How can I do that? and How faster it is compared
to old?

Thanks for you work!