From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5BC7CC433FF for ; Wed, 7 Aug 2019 05:42:49 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 340A821E6C for ; Wed, 7 Aug 2019 05:42:49 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="rDP2IL3m" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 340A821E6C Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-riscv-bounces+infradead-linux-riscv=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=JDHiOXL7NzPuqstdtR5sl59BqMCgMgwjLUeeX3JHtjQ=; b=rDP2IL3mm2fT2/ 1EHktamIBKkh8WDbNxKLndvKuyghXCBuUKWsAFCD7gJT1H89jexGr+CZ3I0XLoo6ELwvERGApM0vj RqyeWF2K9lni94+7xwHWAHvI244NI41iCtG9GdR0MFO1hV9nmJmLSKt5Q1eG58ueo/Pcm9wbWjhEj CcZmKRxXNQzTNNzd0obx3TiVrhqK8EIOkx3fnBKPAehu8MqyXsedie5KKT5nXXU2h5v878dGOc1bP GBsKFpmvEh52Q3JOVT81DXvAnaqwPxWQV++D9zi99IBiQ1s3yPr3/W1tV4phidrqW0gO+BJutby9X L167+lCHE5LYHQA1/6Wg==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hvEil-0002CA-VT; Wed, 07 Aug 2019 05:42:47 +0000 Received: from hch by bombadil.infradead.org with local (Exim 4.92 #3 (Red Hat Linux)) id 1hvEik-0002Bp-3E; Wed, 07 Aug 2019 05:42:46 +0000 Date: Tue, 6 Aug 2019 22:42:46 -0700 From: Christoph Hellwig To: Paul Walmsley Subject: Re: [PATCH] riscv: kbuild: add virtual memory system selection Message-ID: <20190807054246.GB1398@infradead.org> References: <20190802084453.GA1410@infradead.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.11.4 (2019-03-13) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Christoph Hellwig , linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, Alexandre Ghiti Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-riscv" Errors-To: linux-riscv-bounces+infradead-linux-riscv=archiver.kernel.org@lists.infradead.org On Tue, Aug 06, 2019 at 05:02:03PM -0700, Paul Walmsley wrote: > The rationale is to encourage others to start laying the groundwork for > future Sv48 support. The immediate trigger for it was Alex's mmap > randomization support patch series, which needs to set some Kconfig > options differently depending on the selection of Sv32/39/48. Writing a formal todo list is much better encouragement than adding dead code. Th latter has a tendency of lingering around forever and actually hurting people. > > > but actively harmful, which is even worse. > > Reflecting on this assertion, the only case that I could come up with is > that randconfig or allyesconfig build testing could fail. Is this the > case that you're thinking of, or is there a different one? If that's the > one, I do agree that it would be best to avoid this case, and it looks > like there's no obvious way to work around that issue. randconfig or just a user thinking bigger is better and picking it. > > Even if we assume we want to implement Sv48 eventually (which seems > > to be a bit off), we need to make this a runtime choice and not a > > compile time one to not balloon the number of configs that distributions > > (and kernel developers) need to support. > > The expectation is that kernels that support multiple virtual memory > system modes at runtime will probably incur either a performance or a > memory layout penalty for doing so. So performance-sensitive embedded > applications will select only the model that they use, while distribution > kernels will likely take the performance hit for broader single-kernel > support. Even if we want to support Sv39 only or Sv39+Sv39 the choice in the patch doesn't make any sense. So better do the whole thing when its ready than doing false "groundwork". _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv