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

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Date:   Fri, 27 Oct 2023 16:22:24 +0200
From:   J. Neuschäfer <j.neuschaefer@....net>
To:     Nick Terrell <terrelln@...a.com>
Cc:     J. Neuschäfer <j.neuschaefer@....net>,
        Arnd Bergmann <arnd@...db.de>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Russell King <linux@...linux.org.uk>,
        Tony Lindgren <tony@...mide.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Linus Walleij <linus.walleij@...aro.org>,
        Sebastian Reichel <sebastian.reichel@...labora.com>,
        "Hawkins, Nick" <nick.hawkins@....com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Florian Fainelli <f.fainelli@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Xin Li <xin3.li@...el.com>,
        Seung-Woo Kim <sw0312.kim@...sung.com>,
        Paul Bolle <pebolle@...cali.nl>,
        Bart Van Assche <bvanassche@....org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/3] ARM ZSTD boot compression

On Fri, Oct 20, 2023 at 06:53:40PM +0000, Nick Terrell wrote:
> > On Oct 12, 2023, at 6:27 PM, J. Neuschäfer <j.neuschaefer@....net> wrote:
[...]
> > 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.
> 
> I went out and bought a Raspberry Pi 4 to test on. I’ve done some crude measurements
> and see that zstd kernel decompression is just slightly slower than gzip kernel
> decompression, and about 2x slower than lzo. In userspace decompression of the same
> file (a manually compressed kernel image) I see that zstd decompression is significantly
> faster than gzip. So it is definitely something about the preboot boot environment, or how
> the code is compiled for the preboot environment that is causing the issue.
> 
> My next step is to set up qemu on my Pi to try to get some perf measurements of the
> decompression. One thing I’ve really been struggling with, and what thwarted my last
> attempts at adding ARM zstd kernel decompression, was getting preboot logs printed.

Interesting, please keep me updated if you find something out :)

> I’ve figured out I need CONFIG_DEBUG_LL=y, but I’ve yet to actually get any logs.
> And I can’t figure out how to get it working in qemu. I haven’t tried qemu on an ARM
> host with kvm, but that’s the next thing I will try.
> 
> Do you happen to have any advice about how to get preboot logs in qemu? Is it
> possible only on an ARM host, or would it also be possible on an x86-64 host?

I have a patch for that, although I've only used it on real hardware,
AFAIR:

  https://github.com/neuschaefer/linux/commit/f8542094e36652f2c086c76bf20584330aa27711

Assuming, you use ARCH_MULTIPLATFORM, this should help, once you enable
CONFIG_EXPERT.


Thanks

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