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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 C6692C43387 for ; Fri, 18 Jan 2019 12:31:25 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (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 280DB20823 for ; Fri, 18 Jan 2019 12:31:24 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 280DB20823 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 43h0fy0KH1zDr0L for ; Fri, 18 Jan 2019 23:31:22 +1100 (AEDT) Received: from ozlabs.org (bilbo.ozlabs.org [203.11.71.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 43h0bc6hR1zDqwh for ; Fri, 18 Jan 2019 23:28:28 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au Received: by ozlabs.org (Postfix) id 43h0bb6rN7z9sDr; Fri, 18 Jan 2019 23:28:27 +1100 (AEDT) Received: from authenticated.ozlabs.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-256) server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPSA id 43h0bb5dnMz9sDX; Fri, 18 Jan 2019 23:28:27 +1100 (AEDT) From: Michael Ellerman To: Segher Boessenkool Subject: Re: [PATCH 2/4] powerpc/64s: Add slb_full_bitmap rather than hard-coding U32_MAX In-Reply-To: <20190117163017.GS14180@gate.crashing.org> References: <20190117121328.13395-1-mpe@ellerman.id.au> <20190117121328.13395-2-mpe@ellerman.id.au> <20190117163017.GS14180@gate.crashing.org> Date: Fri, 18 Jan 2019 23:28:24 +1100 Message-ID: <87ef9a40bb.fsf@concordia.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linuxppc-dev@ozlabs.org, npiggin@gmail.com Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Segher Boessenkool writes: > On Thu, Jan 17, 2019 at 11:13:26PM +1100, Michael Ellerman wrote: >> The recent rewrite of the SLB code into C included the assumption that >> all CPUs we run on have at least 32 SLB entries. This is currently >> true but a bit fragile as the SLB size is actually defined by the >> device tree and so could theoretically change at any time. > > It also is guaranteed by the architecture, since at least 2.02, FWIW. True. Actually 2.00 says at least 32. Unfortunately we don't live in a world where "the architecture guarantees it" has any bearing on reality :) But given it *should* always be at least 32 maybe I should optimise for that case. We could use a static key to skip the U32_MAX comparison and go down the else path. cheers