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

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Date:   Wed, 8 Feb 2017 16:24:36 -0800
From:   Eric Biggers <ebiggers3@...il.com>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Sven Schmidt <4sschmid@...ormatik.uni-hamburg.de>,
        akpm@...ux-foundation.org, bongkyu.kim@....com,
        rsalvaterra@...il.com, sergey.senozhatsky@...il.com,
        gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
        herbert@...dor.apana.org.au, davem@...emloft.net,
        linux-crypto@...r.kernel.org, anton@...msg.org, ccross@...roid.com,
        keescook@...omium.org, tony.luck@...el.com
Subject: Re: [PATCH v7 0/5] Update LZ4 compressor module

On Thu, Feb 09, 2017 at 08:31:21AM +0900, Minchan Kim wrote:
> 
> Today, I did zram-lz4 performance test with fio in current mmotm and
> found it makes regression about 20%.
> 

This may or may not be the cause of the specific regression you're observing,
but I just noticed that the proposed patch drops a lot of FORCEINLINE
annotations from upstream LZ4.  The FORCEINLINE's are there for a reason,
especially for the main decompression and compression functions which are
basically "templates" that take in different sets of constant parameters, and
should be left in.  We should #define FORCEINLINE to __always_inline somewhere,
or just do a s/FORCEINLINE/__always_inline/g.

Note that the upstream LZ4 code is very carefully optimized, so we should not,
in general, be changing things like when functions are force-inlined, what the
hash table size is, etc.

[Also, for some reason linux-crypto is apparently still not receiving patch 1/5
in the series.  It's missing from the linux-crypto archive at
http://www.spinics.net/lists/linux-crypto/, so it's not just me.]

Thanks!

Eric