From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 4B3ECC2BA1A for ; Wed, 19 Jun 2024 20:45:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=zdrw1HXcfRzkXantfTS7wHoQ7r0VLrtgD6MifONxoRI=; b=R/xR2w0rsxYv2hKb3gzeZQN49g oge0h6qVoHEixqZ7MixYNGrc31EXmakXau0Udgm5mvURrNpqzdreoeim3Eobd9CZIqIZKaqX80zKL Wz6kUZxD+YWqNlu7HO1a69xAqpszYYtYy55j/hFYuKQylDVF3k0Cr5jt3PmGwOf8z3By9z70Tx5po c9OHXPEm8e1IPq8Wfm7dS2NdghTYAV1h3mGBQNpaVguvmrS2tjN6RegQ1rtTNSVzC5NyJw/VC5Egz udzGuxKosZgYI3JPhzBkXnkBpezbKlgxs4QTleDEg8bJWJ7fkeI001LQlOvg+Eq2cc7krbqwHKsGH aL8SMddg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1sK2BV-00000002fgG-0KjM; Wed, 19 Jun 2024 20:45:37 +0000 Received: from casper.infradead.org ([2001:8b0:10b:1236::1]) by bombadil.infradead.org with esmtps (Exim 4.97.1 #2 (Red Hat Linux)) id 1sK2BS-00000002fg4-3Kqd for linux-arm-kernel@bombadil.infradead.org; Wed, 19 Jun 2024 20:45:34 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=zdrw1HXcfRzkXantfTS7wHoQ7r0VLrtgD6MifONxoRI=; b=Cgp8C30k4Feko+f/+cUjJ28F4J 4OSg9BKZN0qZwOZbcnn+rYg689R120F16ETYmztNVIAwaYwC4IEfbnrFWSnVzwHPvgDvdjjNyGWj/ N0D7uaSPTDD+Sc9AU8J+ulX3K6aA9KTi0U1sMM9Air2mx7VXe9UN1GJT98UyhVTGfb5p+2EQEGD6Q NjMMJFIwGw2O2BKTdRMG2/za8Y7Q1yDs7r4v0X2bzAV9TX5Ey+nRjGxKNvMp2Xco/sLYhDzq8++hi GG7yBEQu6DBIbOlbsIx3lHn//HFunckkmN9W/Y3R0H4lJLSOjsiTwVJe1oM5isAa9DJMscWHkW/Ug Db52pD+g==; Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1sK2BR-00000005AQh-0gK8; Wed, 19 Jun 2024 20:45:33 +0000 Date: Wed, 19 Jun 2024 21:45:33 +0100 From: Matthew Wilcox To: Linus Torvalds Cc: Christian Brauner , Al Viro , linux-fsdevel , the arch/x86 maintainers , Linux ARM , Linux Kernel Mailing List Subject: Re: FYI: path walking optimizations pending for 6.11 Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Jun 19, 2024 at 01:25:02PM -0700, Linus Torvalds wrote: > For example, making d_hash() avoid indirection just means that now > pretty much _all_ the cost of __d_lookup_rcu() is in the cache misses > on the hash table itself. Which was always the bulk of it. And on my > arm64 machine, it turns out that the best optimization for the load I > tested would be to make that hash table smaller to actually be a bit > denser in the cache, But that's such a load-dependent optimization > that I'm not doing this. > > Tuning the hash table size or data structure cacheline layouts might > be worthwhile - and likely a bigger deal - but is _not_ what these > patches are about. Funnily, I'm working on rosebush v2 today. It's in no shape to send out (it's failing ~all of its selftests) but *should* greatly improve the cache friendliness of the hash table. And it's being written with the dcache as its first customer.