linux-kernel - Re: [PATCH RFC v3 0/8] kernel-hacking: introduce CONFIG_NO_AUTO

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Message-ID: <20250501150229.GU4439@noisy.programming.kicks-ass.net>
Date: Thu, 1 May 2025 17:02:29 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Brendan Jackman <jackmanb@...gle.com>
Cc: Christoph Hellwig <hch@....de>, chenlinxuan@...ontech.com,
	Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...nel.dk>,
	Sagi Grimberg <sagi@...mberg.me>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Yishai Hadas <yishaih@...dia.com>, Jason Gunthorpe <jgg@...pe.ca>,
	Shameer Kolothum <shameerali.kolothum.thodi@...wei.com>,
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	Alex Williamson <alex.williamson@...hat.com>,
	Peter Huewe <peterhuewe@....de>,
	Jarkko Sakkinen <jarkko@...nel.org>,
	Masahiro Yamada <masahiroy@...nel.org>,
	Nathan Chancellor <nathan@...nel.org>,
	Nicolas Schier <nicolas.schier@...ux.dev>,
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	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>, linux-nvme@...ts.infradead.org,
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	Changbin Du <changbin.du@...el.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH RFC v3 0/8] kernel-hacking: introduce
 CONFIG_NO_AUTO_INLINE

On Thu, May 01, 2025 at 02:19:47PM +0000, Brendan Jackman wrote:
> On Tue Apr 29, 2025 at 12:35 PM UTC, Christoph Hellwig wrote:
> > On Tue, Apr 29, 2025 at 12:06:04PM +0800, Chen Linxuan via B4 Relay wrote:
> >> This series introduces a new kernel configuration option NO_AUTO_INLINE,
> >> which can be used to disable the automatic inlining of functions.
> >> 
> >> This will allow the function tracer to trace more functions
> >> because it only traces functions that the compiler has not inlined.
> >
> > This still feels like a bad idea because it is extremely fragile.
> 
> Can you elaborate on that - does it introduce new fragility?

given it needs to sprinkle __always_inline around where it wasn't needed
before, yeah.

Also, why would you want this? function tracer is already too much
output. Why would you want even more?