From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (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 A6052282EA; Wed, 19 Jun 2024 20:45:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1718829938; cv=none; b=KKqTfgzUUMOrxJnVjqP7SrXTWwpO9ZcEdn4QHjeg3vCXbCko//IIa6YnjQQ0E3AItpA5b/WOi7wmzCRA/H8pQGpaOiSbqiDOlok48lvtMp+6Dz2s2ybH6Z0lqKsi/CI6k49YmCGwdrdzqV8hmllFaPxYrDVc/Kyv5dktQb+7IV8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1718829938; c=relaxed/simple; bh=TS23xKUKQqMPdlikefFBlyBu6PXWq69uofk7oIjoLxs=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Jlu+j3LQYlzhmrttGKh8MUNXz4iVqXFq/NUI905XFyIoHr8HnEaG7Z4Ih+OE5NarmBezO+w85vzmWe2GKuGYmg5u7jo1flG923gYVfcQH5DnmpOlSqytRUS4zP+Nc+SN2VF0nR5FE8AVvHfkJX0T//ljme7kLiYSmuQSdWjGcB0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=Cgp8C30k; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="Cgp8C30k" 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: Precedence: bulk X-Mailing-List: linux-kernel@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 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.