From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from layka.disroot.org (layka.disroot.org [178.21.23.139]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 194DE2DFA5B for ; Tue, 15 Apr 2025 04:03:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=178.21.23.139 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744689799; cv=none; b=VCqKOrGIl146u5RulyemTitAQv9GDR8plL++mKr5wNNX3l00oOUy6Mav9v+ig0cxLgeIM2G7axUthCXyUOGd5Kxuum2HrzOk9X7ilp0/qz/UdaCYBKRtV+9JVQSmqYPXLv+4GrnB1A243bFVj3YOYAesH5SgVV+S1D0gyhQ8S6g= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744689799; c=relaxed/simple; bh=qghY3Q63wlbiOp2xaoqPs+ASXzEZ6WE5IN9CPJW601g=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ejzd0eavXORZf8UR9PxSdeIZPeKeOFWKnZ5KmUSyoySBxo3ogO9nCRj4rFEXychf0u+5he6zJzN56k1t2WHkZLuemMa9SmbH139pJBTsNr4w5Rj8dcmbigA4wUatZGaR5CUsbHc6Fa0lu9i9k+EIpjNEvCFCBGsWuIYuc9HlhmU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=disroot.org; spf=pass smtp.mailfrom=disroot.org; dkim=pass (2048-bit key) header.d=disroot.org header.i=@disroot.org header.b=Ji2SQVyP; arc=none smtp.client-ip=178.21.23.139 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=disroot.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=disroot.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=disroot.org header.i=@disroot.org header.b="Ji2SQVyP" Received: from mail01.disroot.lan (localhost [127.0.0.1]) by disroot.org (Postfix) with ESMTP id C443A25C28; Tue, 15 Apr 2025 06:03:12 +0200 (CEST) X-Virus-Scanned: SPAM Filter at disroot.org Received: from layka.disroot.org ([127.0.0.1]) by localhost (disroot.org [127.0.0.1]) (amavis, port 10024) with ESMTP id i47edZjCi7gj; Tue, 15 Apr 2025 06:03:11 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=disroot.org; s=mail; t=1744689791; bh=qghY3Q63wlbiOp2xaoqPs+ASXzEZ6WE5IN9CPJW601g=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=Ji2SQVyPX74uhW4nzx2gTUfEnQ14bhJ8iRCovvUvoFsfyebI38qdHfWeEbfq6ZZ3v 0ZjxtQAJTY7KZtPH+ssMndJuYPtSr7vdUqI3cAPHS6kphugIyx5iJQLSpjBWoP9tBO Ba3GCaLnsRbYo8GL3YYLtEVMsAVKVQlFHZurAuxFL4VP3KlcX1yiu6l2TUFTYtNmec 2MpGIgStiKmCJcAp07h5v58DHbZckcYsOn5kEbGislDO//yg3OHgR7lTzvuALeE+o2 FLyS8VZi8nkIjEoXTk817if5s5YemP4C6214p4lzeCA8IbOweEAVTpwAMGssnhLGLb 8Zm2LtQNGLD2A== Date: Tue, 15 Apr 2025 04:03:03 +0000 From: Yao Zi To: David Gibson Cc: devicetree-compiler@vger.kernel.org Subject: Re: [RESEND PATCH] flattree: Optimize stringtable_insert() Message-ID: References: <20250412100351.9009-2-ziyao@disroot.org> Precedence: bulk X-Mailing-List: devicetree-compiler@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Tue, Apr 15, 2025 at 11:39:03AM +1000, David Gibson wrote: > On Mon, Apr 14, 2025 at 12:10:09PM +0000, Yao Zi wrote: > > On Mon, Apr 14, 2025 at 04:24:23PM +1000, David Gibson wrote: > > > On Sat, Apr 12, 2025 at 10:03:52AM +0000, Yao Zi wrote: > > > > According to perf result, stringtable_insert() is one of the five hotest > > > > functions, which is obvious since it depends on a brute-force, > > > > quadratic-complexity method to deduplicate the string block and is > > > > called at creation of every property. > > > > > > Right. The optimization strategy of dtc and libfdt is pretty much "if > > > it's slow enough that it bothers someone, then we'll think about it". > > > Little effort has gone into optimization, in general, because device > > > trees are generally so small that runtime hasn't really been a > > > problem, even with very inefficient coding. > > > > > > > This patch optimizes the function in two ways, > > > > > > > > - Replace brute-force deduplication with libc-provided memmem(), which > > > > is guaranteed to be in linear complexity on both glibc on musl libc. > > > > This brings roughly 24.6% reduction in execution time. > > > > > > That said, this is a substantial improvement for a very simple change. > > > I'd be happy to apply this change, separated into its own patch. > > > > > > > - An open-addressing hashtable is maintained to track strings already > > > > inserted. As property names are likely to be duplicated, this could > > > > filter out many existing strings, avoiding traversing the string > > > > block. This reduces another 1.2% of execution time. > > > > > > Honestly the substantial complexity this adds doesn't seem worth it > > > for a mere 1.2% improvement. > > > > Thanks for the feedback. At first I'm only interested in improving the > > deduplication with a hashtable -- but later it's found that reusing > > subsequences is also necessary and memmem() itself surprisingly brings a > > huge improvement. > > > > I'm preparing for v2 where the hashtable is split out and also used for > > optimizing get_node_by_label(). Although the changes are not ready for > > reviewing now, the new optimization reduces executation by another > > 6.4%. Do you think it's a reason strong enough to keep the the code? > > Probably not, unless you can convince me there's a use case where the > performance is a pressing practical problem. Okay, I'll keep only the memmem() change in v2. > > Here's a summary of the changes, > > > > Makefile.dtc | 1 + > > checks.c | 4 -- > > dtc-parser.y | 4 +- > > dtc.c | 4 ++ > > dtc.h | 19 +++++++ > > flattree.c | 68 +++++++++++++++++++------ > > hashtable.c | 141 +++++++++++++++++++++++++++++++++++++++++++++++++++ > > livetree.c | 35 +++++++++++-- > > 8 files changed, 251 insertions(+), 25 deletions(-) > > > > ... > > > > > > Best regards, > > Yao Zi > > > > -- > David Gibson (he or they) | I'll have my music baroque, and my code > david AT gibson.dropbear.id.au | minimalist, thank you, not the other way > | around. > http://www.ozlabs.org/~dgibson Thanks, Yao Zi