From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: About LPAE supporting on EXYNOS5440 Date: Wed, 12 Jun 2013 11:58:20 +0200 Message-ID: <201306121158.20676.arnd@arndb.de> References: <109e01ce667e$5becc880$13c65980$%kim@samsung.com> <15605927.1Yi6Xe5hWs@wuerfel> <51B7FD2E.9030306@gmail.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Return-path: Received: from moutng.kundenserver.de ([212.227.126.187]:59560 "EHLO moutng.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751454Ab3FLJ7B (ORCPT ); Wed, 12 Jun 2013 05:59:01 -0400 In-Reply-To: <51B7FD2E.9030306@gmail.com> Sender: linux-samsung-soc-owner@vger.kernel.org List-Id: linux-samsung-soc@vger.kernel.org To: Subash Patel Cc: Kukjin Kim , 'Olof Johansson' , linux-samsung-soc@vger.kernel.org, linux-arm-kernel@lists.infradead.org On Wednesday 12 June 2013, Subash Patel wrote: > > I would definitely leave on exynos5440 support in defconfig. It's not a > > lot of extra code, and if you have a system with less than 4GB memory, > > you really don't want to enable LPAE because of the overhead. > > Even if we have <= 4GB memory, and the system designers have placed the > memory banks in addresses > 2^32 bytes, then we need LPAE support. I > think we may have such systems in future. So memory capacity is not the > only parameter to judge if we need to enable LPAE or not. Yes, but that wasn't the point. You can always build systems with exynos5440 that don't need LPAE, so we should not assume that it is not a reasonable configuration. I would certainly advise system designers to put all the RAM and I/O into normally addressable locations if possible to avoid the need for LPAE, but of course that isn't always possible. We should probably have someone measure the performance impact of LPAE as well. If it's less than a few percent, we might not care all that much. Arnd From mboxrd@z Thu Jan 1 00:00:00 1970 From: arnd@arndb.de (Arnd Bergmann) Date: Wed, 12 Jun 2013 11:58:20 +0200 Subject: About LPAE supporting on EXYNOS5440 In-Reply-To: <51B7FD2E.9030306@gmail.com> References: <109e01ce667e$5becc880$13c65980$%kim@samsung.com> <15605927.1Yi6Xe5hWs@wuerfel> <51B7FD2E.9030306@gmail.com> Message-ID: <201306121158.20676.arnd@arndb.de> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Wednesday 12 June 2013, Subash Patel wrote: > > I would definitely leave on exynos5440 support in defconfig. It's not a > > lot of extra code, and if you have a system with less than 4GB memory, > > you really don't want to enable LPAE because of the overhead. > > Even if we have <= 4GB memory, and the system designers have placed the > memory banks in addresses > 2^32 bytes, then we need LPAE support. I > think we may have such systems in future. So memory capacity is not the > only parameter to judge if we need to enable LPAE or not. Yes, but that wasn't the point. You can always build systems with exynos5440 that don't need LPAE, so we should not assume that it is not a reasonable configuration. I would certainly advise system designers to put all the RAM and I/O into normally addressable locations if possible to avoid the need for LPAE, but of course that isn't always possible. We should probably have someone measure the performance impact of LPAE as well. If it's less than a few percent, we might not care all that much. Arnd