From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:36452) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XEI3S-0003WY-Uh for qemu-devel@nongnu.org; Mon, 04 Aug 2014 09:12:04 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XEI3L-00024p-Ur for qemu-devel@nongnu.org; Mon, 04 Aug 2014 09:11:58 -0400 Received: from smtp.codeaurora.org ([198.145.11.231]:54068) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XEI3L-00024H-OZ for qemu-devel@nongnu.org; Mon, 04 Aug 2014 09:11:51 -0400 Message-ID: <53DF8694.4040107@codeaurora.org> Date: Mon, 04 Aug 2014 09:11:48 -0400 From: Christopher Covington MIME-Version: 1.0 References: <1406733627-24255-1-git-send-email-alex.bennee@linaro.org> <87bns0lf9j.fsf@linaro.org> In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH v2 0/5] AArch64 TLB performance improvements List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Maydell Cc: =?UTF-8?B?QWxleCBCZW5uw6ll?= , QEMU Developers On 08/04/2014 06:32 AM, Peter Maydell wrote: > On 4 August 2014 11:23, Alex Benn=C3=A9e wrote= : >> Peter Maydell writes: >>> So: >>> * there's clearly a big perf win to be had here >>> * this patchset gives us that for 4K pages on AArch64 >>> * but it doesn't help for 4K pages on AArch32 (really >>> common) >> >> Well for the AArch32 profile if you ran under qemu-system-aarch64 you >> would be OK surely? >=20 > Yes, but that's pretty non-obvious, and also it doesn't > make much sense to the user to say "these 32 bit > CPUs should be run under qemu-system-aarch64 but > these other ones should be under qemu-system-arm". >=20 >>> * and it's not going to be good for 64K pages on AArch64 >>> either (which I suspect will not be a rare choice) >> >> Does the kernel already use 64k pages for it's code? >=20 > There's a config option, which will cause it to use 64K > pages for everything including userspace. > (There's also 16K pages but I forget if Linux has support > for those.) I think the kernel can also use 64K pages in > some cases even in a 4K page config, but I don't know the > details. Linux support for the 16K granule has not been merged nor have I seen any patches for it. With a 4K granule one can early out to 1GiB blocks ("gigabyte kernel logi= cal mappings") [1] or 2MiB blocks ("huge pages") [2]. With a 64K granule, one can early out to 512MiB blocks ("huge pages") [2]= . 1. http://permalink.gmane.org/gmane.linux.ports.arm.kernel/322436 2. http://comments.gmane.org/gmane.linux.kernel.mm/100651 Regards, Christopher --=20 Employee of Qualcomm Innovation Center, Inc. Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by the Linux Foundation.