From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 269EA53B9; Mon, 12 Dec 2022 20:06:18 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0BBCFC433EF; Mon, 12 Dec 2022 20:06:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1670875578; bh=X5xmfWRTmgqPRq7JxHELTB+1YzEZLrNIUjkjESAieLE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=hjhQE9tSqE1qG14JX44LeNEEuvaTD1RKr5NzuJgBYdyUc5X5zx/nevMdch4cMHqla aET/T9m9eKSjPgNnLkPHHRf3GoAQKdpx0xmBPT+1mu/v66c/rn9/76lMesQddph8TV ODoeJUeeRFXXLdiksvfnZivLkbRw9O9MrYuk14fhCE1zlelcjPgNMee/2ti9TcqcJW Xi6JgrXtj8RJF73XhawyUPXap8Us/RLe/BPFcre5Dhu7g8VZ26du8pE44KPMW6XJ+r Lvp0UNErnPuJ3+lFMl0I3/DAAJMZkslbHbweunIJE4sBZ2xfQhTDwyayALW84Pe52r v6AwKjJzVO0dA== Date: Mon, 12 Dec 2022 13:06:16 -0700 From: Nathan Chancellor To: Daniel Jordan Cc: Masahiro Yamada , Nick Desaulniers , Tom Rix , Nicolas Schier , Sami Tolvanen , Vincent Donnefort , linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev, patches@lists.linux.dev, Steffen Klassert , linux-crypto@vger.kernel.org Subject: Re: [PATCH v2 1/2] padata: Mark padata_work_init() as __ref Message-ID: References: <20221207191657.2852229-1-nathan@kernel.org> <20221207191657.2852229-2-nathan@kernel.org> <20221212192157.plxiyyinfhieyzbt@parnassus.localdomain> Precedence: bulk X-Mailing-List: llvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221212192157.plxiyyinfhieyzbt@parnassus.localdomain> On Mon, Dec 12, 2022 at 02:21:57PM -0500, Daniel Jordan wrote: > On Mon, Dec 12, 2022 at 10:05:02AM -0700, Nathan Chancellor wrote: > > On Mon, Dec 12, 2022 at 10:07:24PM +0900, Masahiro Yamada wrote: > > > I am not sure if the compiler should do this level of optimization > > > because kernel/padata.c does not seem to be a special case. > > > Perhaps, we might be hit with more cases that need __ref annotation, > > > which is only required by LTO. > > > > That's possible. I did only see this once instance in all my builds but > > allmodconfig + ThinLTO might not be too interesting of a case, > > since the sanitizers will be enabled, which makes optimization more > > difficult. I could try to enable ThinLTO with some distribution > > configurations to see if there are any more instances that crop up. > > Yes, if there were many more instances of this problem it might be worth > thinking about an LTO-specific solution to fix it closer to the source. Ack, I will wire up some build tests to see if this optimization occurs frequently enough to warrant a wider fix. > > > One note is that, we could discard padata_work_init() > > > because (1) and (3) are both annotated as __init. > > > So, another way of fixing is > > > static __always_inline void padata_work_init(...) > > > because the compiler would determine padata_work_init() > > > would be small enough if the caller and callee belonged to > > > the same section. > > > > > > I do not have a strong opinion. > > I'm right there with you. :-) > > > > Honestly, I do not know what the best approach would be to fix this. > > Either approach works, either can include an explanatory comment. > __ref seems more targeted to the problem at hand. Right, I suspect __ref is the right way to go for this particular issue. I will add a comment regardless. > > > If we go with the __ref annotation, I can pick this, but > > > at least can you add some comments? > > > > > > > > > include/linux/init.h says: > > > "optimally document why the __ref is needed and why it's OK" > > > > > > > > > I think this is the case that needs some comments > > > because LTO optimization looks too tricky to me. > > > > Sure thing, I will send a v3 either Tuesday or Wednesday with an updated > > commit message and code comment if we end up going this route. > > A nitpick, but as long as you're respinning, if we stay with this > approach, could you put __ref just before the function name? init.h > says "The markers follow same syntax rules as __init / __initdata" and > for those it says "You should add __init immediately before the function > name" though there are plenty of places in the tree that don't do this. Sure thing! Cheers, Nathan