From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (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 CDED1232379 for ; Wed, 11 Dec 2024 14:04:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733925847; cv=none; b=EGRlg3sPMfymmCDPABuepK8uLtk7b/S6P1wiSVcdNcQd+gxYFiO/hLjxCV9yx0LTXJqblerEqX8JJIs9YnMIZDYEHLLAazq7pPwC+dvfpqZIhuvu0VLhicGbwnGcvXF701YN5MPTkz170xYgNV4Ee7OQoZMXxkBq+2dieViGDdU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733925847; c=relaxed/simple; bh=uig1fxNOcNQk4L4DcKA96S4K1+tjKyUesavchLaLiC8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=J9IRNjjECEPrmxuO8lYDSfXUGwmju5QYjNHQPWF8JA8bTsITm60lHDtKlM4+XqAmKsfZm5CZOrJo48agpj/iYzyxDasdLhUgUUOqheI2shRJ3bvaymslwHbmoUf8nvrGpb+zvc9RalskG7NJGw2j61takDJuWKB91vVnBcZUbB8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=kWVLS6d4; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=OKKVRjHg; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="kWVLS6d4"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="OKKVRjHg" Date: Wed, 11 Dec 2024 15:04:02 +0100 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1733925844; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=UsNEwFWdf8+xj8apQ2tpCjXCCbHBW+SvnxbyipiMG7c=; b=kWVLS6d4m+EdcwV3DiEN+Tq0iCErqJGk2iwi7xF+AVXRlYxWVxHuSBbykXREOtAi1RWMQA 8ayx646x4C82OrGgSupCiDY55xXdldBUUmGU/RAvhqvBKsgO8r29iOc8gOtKb2QMTmxoTV Boe4qN6fO+Kl8Ciz820pgNZ5sK/hKM262a/Ahb+qUNK1h4zkPb0LcGYp1n+mN0jlYg0GEk qm8hRO8nm9alfzkHePtvVRTB9ZaFJiNoE7Q7j9+N++paHbPLmus4EffeRREhL4VG6ZF/Id 8/CqVJUwrr6vpTPzNWFUIrp+TFHPjA7pNNcNlDoqSoduukWH+JIFzbNaYYY4NA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1733925844; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=UsNEwFWdf8+xj8apQ2tpCjXCCbHBW+SvnxbyipiMG7c=; b=OKKVRjHggoTfjau/0sKye5pPUjMe8nsbgsOCCpYuo4jyTYQistgxgsYQz4pnoDQjFIFnH7 FAG0k5Ffj1lb+UDw== From: Sebastian Andrzej Siewior To: Arnd Bergmann Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Arnd Bergmann , linux-mm@kvack.org, linux-rt-devel@lists.linux.dev, Ard Biesheuvel , Clark Williams , Jason Baron , Josh Poimboeuf , Linus Walleij , Mark Rutland , Matthew Wilcox , Peter Zijlstra , Russell King , Steven Rostedt Subject: Re: [PATCH 2/4] ARM: Disable HIGHPTE on PREEMPT_RT kernels Message-ID: <20241211140402.yf7gMExr@linutronix.de> References: <20241210160556.2341497-1-arnd@kernel.org> <20241210160556.2341497-3-arnd@kernel.org> <20241211134811.wM_UADhQ@linutronix.de> 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=utf-8 Content-Disposition: inline In-Reply-To: <20241211134811.wM_UADhQ@linutronix.de> On 2024-12-11 14:48:11 [+0100], To Arnd Bergmann wrote: > I guess if you have boxes with 4GiB+ and can proof that the performance > improves without HIGHPTE (since you don't have to map the page table). > The question is then how much of low mem has to be used instead and when > does it start to hurt. Some numbers have been been documented in commit 14315592009c1 ("x86, mm: Allow highmem user page tables to be disabled at boot time") and I would like cite: | We could probably handwave up an argument for a threshold at 16G of total | RAM. which means HIGHPTE would make sense with >= 16GiB of memory. Sebastian