Re: [PATCH 0/3] ARM ZSTD boot compression

From: "Jonathan Neuschäfer" <j.neuschaefer@gmx.net>
To: Arnd Bergmann <arnd@arndb.de>
Cc: "Jonathan Neuschäfer" <j.neuschaefer@gmx.net>,
	linux-arm-kernel@lists.infradead.org,
	"Russell King" <linux@armlinux.org.uk>,
	"Nick Terrell" <terrelln@fb.com>,
	"Tony Lindgren" <tony@atomide.com>,
	"Geert Uytterhoeven" <geert+renesas@glider.be>,
	"Linus Walleij" <linus.walleij@linaro.org>,
	"Sebastian Reichel" <sebastian.reichel@collabora.com>,
	"Hawkins, Nick" <nick.hawkins@hpe.com>,
	"Christophe Leroy" <christophe.leroy@csgroup.eu>,
	"Florian Fainelli" <f.fainelli@gmail.com>,
	"Nick Desaulniers" <ndesaulniers@google.com>,
	"Xin Li" <xin3.li@intel.com>,
	"Seung-Woo Kim" <sw0312.kim@samsung.com>,
	"Paul Bolle" <pebolle@tiscali.nl>,
	"Bart Van Assche" <bvanassche@acm.org>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/3] ARM ZSTD boot compression
Date: Sat, 15 Apr 2023 00:50:01 +0200	[thread overview]
Message-ID: <ZDnYme3w3T6310MJ@probook> (raw)
In-Reply-To: <9ae523ae-aad4-40b1-8b6b-d5e18bf8b92a@app.fastmail.com>

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On Wed, Apr 12, 2023 at 11:33:15PM +0200, Arnd Bergmann wrote:
> On Wed, Apr 12, 2023, at 23:21, Jonathan Neuschäfer wrote:
> > This patchset enables ZSTD kernel (de)compression on 32-bit ARM.
> > Unfortunately, it is much slower than I hoped (tested on ARM926EJ-S):
> >
> >  - LZO:  7.2 MiB,  6 seconds
> >  - ZSTD: 5.6 MiB, 60 seconds
> 
> That seems unexpected, as the usual numbers say it's about 25%
> slower than LZO. Do you have an idea why it is so much slower
> here?

No clear idea.

I guess it might be related to caching or unaligned memory accesses
somehow.

I suspected CONFIG_CPU_DCACHE_WRITETHROUGH, which was enabled, but
disabling it didn't improve performance.

> How long does it take to decompress the generated arch/arm/boot/Image
> file in user space on the same hardware using lzop and zstd?

Unfortunately, the unzstd userspace tool requires a buffer of of 128 MiB
(the window size), which is too big for my usual devboard (which has about
100 MiB available). I'd have to test on a different board.

Jonathan

---
# uname -a
Linux buildroot 6.3.0-rc6-00020-g023058d50f2f #1212 PREEMPT Fri Apr 14 20:58:21 CEST 2023 armv5tejl GNU/Linux

# ls -lh
total 13M
-rw-r--r--    1 root     root        7.5M Jan  1 00:07 piggy.lzo
-rw-r--r--    1 root     root        5.8M Jan  1 00:07 piggy.zstd

# time lzop -d piggy.lzo -c > /dev/null
lzop: piggy.lzo: warning: ignoring trailing garbage in lzop file
Command exited with non-zero status 2
real    0m 3.38s
user    0m 3.20s
sys     0m 0.18s

# time unzstd piggy.zstd -c > /dev/null
[  858.270000] __vm_enough_memory: pid: 114, comm: unzstd, not enough memory for the allocation
piggy.zstd : Decoding error (36) : Allocation error : not enough memory
Command exited with non-zero status 1
real    0m 0.03s
user    0m 0.01s
sys     0m 0.03s

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