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Thu, 21 May 2020 15:56:31 +0000 (GMT) Date: Thu, 21 May 2020 18:56:29 +0300 From: Mike Rapoport To: Russell King - ARM Linux admin Subject: Re: [PATCH 0/2] ARM: Allow either FLATMEM or SPARSEMEM on the multiplatform build Message-ID: <20200521155629.GT1059226@linux.ibm.com> References: <20200521081825.1348844-1-rppt@linux.ibm.com> <20200521120308.GR1551@shell.armlinux.org.uk> <20200521123327.GQ1059226@linux.ibm.com> <20200521140745.GS1059226@linux.ibm.com> <20200521145020.GS1551@shell.armlinux.org.uk> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200521145020.GS1551@shell.armlinux.org.uk> X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.216, 18.0.676 definitions=2020-05-21_08:2020-05-21, 2020-05-21 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 adultscore=0 malwarescore=0 mlxlogscore=999 impostorscore=0 phishscore=0 cotscore=-2147483648 suspectscore=0 bulkscore=0 spamscore=0 clxscore=1015 mlxscore=0 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2005210112 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200521_085649_570489_6F1B18BA X-CRM114-Status: GOOD ( 31.76 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Florian Fainelli , Arnd Bergmann , Stephen Boyd , Kevin Cernekee , Doug Berger , Gregory Fong , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, May 21, 2020 at 03:50:20PM +0100, Russell King - ARM Linux admin wrote: > On Thu, May 21, 2020 at 05:07:45PM +0300, Mike Rapoport wrote: > > On Thu, May 21, 2020 at 03:33:29PM +0300, Mike Rapoport wrote: > > > On Thu, May 21, 2020 at 01:03:08PM +0100, Russell King - ARM Linux admin wrote: > > > > On Thu, May 21, 2020 at 11:18:23AM +0300, Mike Rapoport wrote: > > > > > (resendig for the correct address and with mailing list cc'ed, sorry for > > > > > the noise) > > > > > > > > > > Hi, > > > > > > > > > > Following the discussion at [1], I'm resending the patches that enable > > > > > memory model selection in menuconfig and such. > > > > > > > > > > These patches do not change the way the configuration is generated from the > > > > > defconfigs and they do not change explicit selection of SPARSEMEM for > > > > > platforms that have "select ARCH_ENABLE_SPARSEMEM". > > > > > > > > > > The mere change is that when a user runs an interactive configuration they > > > > > will be allowed to select between FLATMEM and SPARSMEM, which is not the > > > > > case today. > > > > > > > > > > There is indeed some awkwardness in, e.g. removal of > > > > > ARCH_SPARSEMEM_DEFAULT, but this is what memory model selection logic in > > > > > mm/Kconfig imposes. > > > > > > > > > Right, but the question is whether we want to offer flatmem for rpc. > > > > It isn't allowed today, and so far no one has said why it's a > > > > desirable change to make. > > > > > > With ARCH_RPC=y (or ARCH_SA1100 or ARCH_EP93XX for that matter) > > > ARCH_MULTIPLATFORM=n which prevents ARCH_SELECT_MEMORY_MODEL from being > > > enabled and since any of these machines explicitly selects > > > ARCH_SPARSEMEM_ENABLE, the only available memory model would be > > > SPARSEMEM. > > > > > > I played a bit with menuconfig and if any of the platforms requiring > > > sparsemem is selected, the menu allowing the user to choose the memory > > > model disappears. > > > > Ah, when either of these patforms will become a part of the > > multiplatform build, the only option for multiplatform build will be > > sparsemem. > > So it would be nice if somebody could check the cost of using sparsemem > > vs flatmem, espessially on low end machines. > > Do you think they will become part of multiplatform? > > If they're low-end machines, then adding: > > (a) the additional memory overhead of a multiplatform kernel > (b) the additional runtime overhead of the complexities of multiplatform > kernels > > is surely an odd thing to do, especially when few really care about > these platforms becoming part of a multiplatform kernel, except those > who like the idea of multiplat. I honestly don't know, it was Arnd who was talking about adding ep93xx to multiplat. So, probably better phrasing would have been "if either of these patforms will become a part of the multiplatform build...". Anyway, benchmarking sparsemem vs flatmem on a platform that is already a part of multiplat might be useful to understand whether we need both of them or we can simply make everything use sparsemem. > -- > RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ > FTTC for 0.8m (est. 1762m) line in suburbia: sync at 13.1Mbps down 424kbps up -- Sincerely yours, Mike. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel