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

From: "J. Neuschäfer" <j.neuschaefer@gmx.net>
To: Nick Terrell <terrelln@meta.com>
Cc: "Jonathan Neuschäfer" <j.neuschaefer@gmx.net>,
	"Arnd Bergmann" <arnd@arndb.de>,
	"Linux ARM" <linux-arm-kernel@lists.infradead.org>,
	"Russell King" <linux@armlinux.org.uk>,
	"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 Mailing List" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 0/3] ARM ZSTD boot compression
Date: Fri, 13 Oct 2023 03:27:12 +0200	[thread overview]
Message-ID: <ZSic8JsHGIlfuwhp@probook> (raw)
In-Reply-To: <1C6CE84E-557D-4436-BF13-E7275DE390A8@meta.com>

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On Thu, Oct 12, 2023 at 10:33:23PM +0000, Nick Terrell wrote:
> > On Apr 14, 2023, at 10:00 PM, Jonathan Neuschäfer <j.neuschaefer@gmx.net> wrote:
> > On Thu, Apr 13, 2023 at 01:13:21PM +0200, Arnd Bergmann wrote:
> >> On Wed, Apr 12, 2023, at 23:33, 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
[...]
> > For ZSTD as used in kernel decompression (the zstd22 configuration), the
> > window is even bigger, 128 MiB. (AFAIU)
> 
> Sorry, I’m a bit late to the party, I wasn’t getting LKML email for some time...
> 
> But this is totally configurable. You can switch compression configurations
> at any time. If you believe that the window size is the issue causing speed
> regressions, you could use a zstd compression to use a e.g. 256KB window
> size like this:
> 
>   zstd -19 --zstd=wlog=18
> 
> This will keep the same algorithm search strength, but limit the decoder memory
> usage.

Noted.

> I will also try to get this patchset working on my machine, and try to debug.
> The 10x slower speed difference is not expected, and we see much better speed
> in userspace ARM. I suspect it has something to do with the preboot environment.
> E.g. when implementing x86-64 zstd kernel decompression, I noticed that
> memcpy(dst, src, 16) wasn’t getting inlined properly, causing a massive performance
> penalty.

In the meantime I've seen 8s for ZSTD vs. 2s for other algorithms, on
only mildly less ancient hardware (Hi3518A, another ARM9 SoC), so I
think the main culprit here was particularly bad luck in my choice of
test hardware.

The inlining issues are a good point, noted for the next time I work on this.

Thanks,
Jonathan

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