linux-kernel - Re: [PATCH v4 0/7] lib/lzo: performance improvements

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Message-ID: <fba24452-ae3a-0caa-11b4-aea69abf2fff@arm.com>
Date:   Fri, 7 Dec 2018 15:54:07 +0000
From:   Dave Rodgman <dave.rodgman@....com>
To:     "Markus F.X.J. Oberhumer" <markus@...rhumer.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
CC:     "herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
        "davem@...emloft.net" <davem@...emloft.net>,
        Matt Sealey <Matt.Sealey@....com>,
        "nitingupta910@...il.com" <nitingupta910@...il.com>,
        "minchan@...nel.org" <minchan@...nel.org>,
        "sergey.senozhatsky.work@...il.com" 
        <sergey.senozhatsky.work@...il.com>,
        "sonnyrao@...gle.com" <sonnyrao@...gle.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        nd <nd@....com>, "sfr@...b.auug.org.au" <sfr@...b.auug.org.au>
Subject: Re: [PATCH v4 0/7] lib/lzo: performance improvements

Hi Markus,

On 06/12/2018 3:47 pm, Markus F.X.J. Oberhumer wrote:> Request 3 - add lzo-rle; *NOT* acked by me
 >
 >     [PATCH 6/8] lib/lzo: implement run-length encoding
 >     [PATCH 7/8] lib/lzo: separate lzo-rle from lzo
 >     [PATCH 8/8] zram: default to lzo-rle instead of lzo
 >
 > It (1) silently changes the compressed data format

I'm not sure this is relevant: as a separate algorithm, there's no reason
to retain the same format (although backwards compatibility can help with
migration). If you know of a way to improve the compatibility aspect
though, that would be great!

 > (2) crashes on MIPS,

Please could you provide more detail? I tested on x86-32, x86-64, arm,
arm64 and big-endian MIPS64, but if there is an issue I missed I'd like to
address it.

 > and (3) makes compression and decompression on typical data 10% slower on
 > X86_64 with our internal benchmarks,

It is of course data-dependent. In my testing, as I mentioned previously, RLE
without the other patches does regress slightly on high-entropy data, but
offers a win on low-entropy data. For the right applications (e.g., zram),
this makes it overall beneficial.

 > and (4) has to be carefully checked for buffer overflows.

This has been reviewed prior to sharing on LKML, and of course tested,
but further review is of course welcome.

 > As a final comment, I question the quality your benchmarks - combining
 > arch-related ARM64 improvements and algorithmic changes into one
 > benchmark comparision is just unprofessional marketing.

I felt it was helpful to show overall performance with the complete patchset:
this is what end-users experience. However, as you can see below, I also
previously shared a summary of the two main components of the patchset to
try and address this sort of concern:

 >> As a quick summary of the impact of these patches on bigger chunks of
 >> data, I've compared the performance of four different variants of lzo
 >> on two large (~40 MB) files. The numbers show round-trip throughput
 >> in MB/s:
 >>
 >> Variant         | Low-entropy | High-entropy
 >> Current lzo     |  242        | 157
 >> Arm opts        |  290        | 159
 >> RLE             |  876        | 151
 >> Arm opts + RLE  | 1150        | 181

cheers

Dave