linux-kernel - Re: [PATCH v3 3/8] lib: add zstd support to decompress

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Message-ID: <20200326164732.GA17157@ntb.petris.klfree.czf>
Date:   Thu, 26 Mar 2020 17:47:32 +0100
From:   Petr Malat <oss@...at.biz>
To:     Nick Terrell <nickrterrell@...il.com>
Cc:     Nick Terrell <terrelln@...com>, linux-kernel@...r.kernel.org,
        Chris Mason <clm@...com>, linux-kbuild@...r.kernel.org,
        x86@...nel.org, gregkh@...uxfoundation.org,
        Kees Cook <keescook@...omium.org>,
        Kernel Team <Kernel-team@...com>,
        Adam Borowski <kilobyte@...band.pl>,
        Patrick Williams <patrickw3@...com>, rmikey@...com,
        mingo@...nel.org, Patrick Williams <patrick@...cx.xyz>
Subject: Re: [PATCH v3 3/8] lib: add zstd support to decompress

Hi!
On Wed, Mar 25, 2020 at 12:58:44PM -0700, Nick Terrell wrote:
> From: Nick Terrell <terrelln@...com>
> * Add unzstd() and the zstd decompress interface.
Here I do not understand why you limit the window size to 8MB even when
you read a larger value from the header. I do not see a reason why there
should be such a limitation at the first place and if there should be,
why it differs from ZSTD_WINDOWLOG_MAX.

I removed that limitation to be able to test it in my environment and I
found the performance is worst than with my patch by roughly 20% (on
i7-3520M), which is a major drawback considering the main motivation
to use zstd is the decompression speed. I will test on arm as well and
share the result tomorrow.
  Petr