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[88.21.205.47]) by smtp.gmail.com with ESMTPSA id u62sm2051825wmu.17.2020.02.26.00.51.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 26 Feb 2020 00:51:02 -0800 (PST) Subject: Re: Sudden slowdown of ARM emulation in master To: Peter Maydell References: From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Message-ID: <99625cab-71ff-a925-fbed-28120f046f0c@redhat.com> Date: Wed, 26 Feb 2020 09:51:01 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.81 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Richard Henderson , QEMU Developers , Niek Linnenbank , qemu-arm , Paolo Bonzini , Igor Mammedov Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 2/26/20 9:48 AM, Peter Maydell wrote: > On Wed, 26 Feb 2020 at 08:44, Philippe Mathieu-Daud=C3=A9 wrote: >> >> On 2/26/20 9:41 AM, Peter Maydell wrote: >>> On Tue, 25 Feb 2020 at 23:08, Niek Linnenbank wrote: >>> >>>> Just now I was working on some small fixes for the cubieboard machine = and rebasing my Allwinner H3 branches. >>>> While doing some testing, I noticed that suddenly the machines were mu= ch slower than before. >>>> I only see this happening when I rebase to this commit: >>>> ca6155c0f2bd39b4b4162533be401c98bd960820 ("Merge tag 'patchew/202= 00219160953.13771-1-imammedo@redhat.com' of https://github.com/patchew-proj= ect/qemu into HEAD") >>> >>> Yeah, I noticed a slowdown yesterday as well, but haven't tracked it do= wn >>> as yet. The first thing would be to do a git bisect to try to narrow >>> down what commit caused it. >> >> My guess: biggest chunk of memory is the DRAM, registered as "fast RAM" >> by QEMU, but the SoCs provide SRAM which is supposed to be faster. Not >> anymore with QEMU. And Linux try to use the SRAM when possible. >=20 > Doesn't sound very likely to me: generally Linux doesn't use random small > lumps of SRAM, it just goes for whatever the dtb says is the main RAM, > usually DRAM. And I thought that all RAM blocks within QEMU performed > the same? >=20 > From the commit that Howard tracked down as the cause it looks like > an ordering-of-actions issue in vl.c where something that was assuming > memory-size-related stuff was set up is now running before those > variables/fields are set correctly rather than after ? Yes, I just saw Howard's email and was going to reply to my own "I'm=20 probably wrong since the mac99 machine doesn't use SRAM".