linux-kernel - Re: [PATCH v4 13/13] riscv: Add qspinlock support

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Message-ID: <CAHVXubiy3=bEf29qpzGX0MoBXkjBy38p9Xhz7yRYN5Sr3qRw0g@mail.gmail.com>
Date: Tue, 27 Aug 2024 10:02:30 +0200
From: Alexandre Ghiti <alexghiti@...osinc.com>
To: Andrew Jones <ajones@...tanamicro.com>
Cc: Guo Ren <guoren@...nel.org>, Alexandre Ghiti <alex@...ti.fr>, Jonathan Corbet <corbet@....net>, 
	Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>, 
	Albert Ou <aou@...s.berkeley.edu>, Conor Dooley <conor@...nel.org>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Andrea Parri <parri.andrea@...il.com>, 
	Nathan Chancellor <nathan@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Will Deacon <will@...nel.org>, Waiman Long <longman@...hat.com>, Boqun Feng <boqun.feng@...il.com>, 
	Arnd Bergmann <arnd@...db.de>, Leonardo Bras <leobras@...hat.com>, linux-doc@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-riscv@...ts.infradead.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH v4 13/13] riscv: Add qspinlock support

Hi drew,

On Wed, Aug 21, 2024 at 2:18 PM Andrew Jones <ajones@...tanamicro.com> wrote:
>
> On Sat, Aug 17, 2024 at 01:08:34PM GMT, Guo Ren wrote:
> ...
> > > So I have just checked the size of the jump table section:
> > >
> > > * defconfig:
> > >
> > > - ticket: 26928 bytes
> > > - combo: 28320 bytes
> > >
> > > So that's a ~5% increase.
> > >
> > > * ubuntu config
> > >
> > > - ticket: 107840 bytes
> > > - combo: 174752 bytes
> > >
> > > And that's a ~62% increase.
> > The size of the jump table section has increased from 5% to 62%. I
> > think some configuration triggers the jump table's debug code. If it's
> > not a debugging configuration, that's a bug of the Ubuntu config.
>
> And I just remembered we wanted to check with CONFIG_CC_OPTIMIZE_FOR_SIZE

Here we go!

The size of the jump table section:

* defconfig:

- ticket: 12176 bytes
- combo: 13168 bytes

So that's a ~8% increase.

* ubuntu config

- ticket:   73920 bytes
- combo: 84656 bytes

And that's a ~14% increase.

This is the ELF size difference between ticket and combo spinlocks:

* ticket:   695906872 bytes
* combo: 697558496 bytes

So that's an increase of ~0.23% on the ELF.

And the .text section size:

* ticket:   10322820 bytes
* combo: 10332136 bytes

And that's a ~0.09% increase!

So that's even better :)

Thanks for asking!

Alex

>
> Thanks,
> drew
>
> >
> > >
> > > This is the ELF size difference between ticket and combo spinlocks:
> > >
> > > * ticket: 776915592 bytes
> > > * combo: 786958968 bytes
> > >
> > > So that's an increase of ~1.3% on the ELF.
> > >
> > > And the .text section size:
> > >
> > > * ticket: 12290960 bytes
> > > * combo: 12366644 bytes
> > >
> > > And that's a ~0.6% increase!
> > >
> > > Finally, I'd say the impact is very limited :)
> > >
> > > Thanks,
> > >
> > > Alex
> > >
> > >