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 737E1C61CE4 for ; Sat, 19 Jan 2019 10:28:44 +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 28A942086D for ; Sat, 19 Jan 2019 10:28:43 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 28A942086D 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 43hYty0qllzDqSm for ; Sat, 19 Jan 2019 21:28:42 +1100 (AEDT) Received: from ozlabs.org (bilbo.ozlabs.org [IPv6:2401:3900:2:1::2]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 43hYsM6twbzDq7X for ; Sat, 19 Jan 2019 21:27:19 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au Received: by ozlabs.org (Postfix) id 43hYsM695fz9sBQ; Sat, 19 Jan 2019 21:27:19 +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 43hYsM4ZLHz9s2P; Sat, 19 Jan 2019 21:27:19 +1100 (AEDT) From: Michael Ellerman To: Michal =?utf-8?Q?Such=C3=A1nek?= Subject: Re: [PATCH 4/4] powerpc/64s: Support shrinking the SLB for debugging In-Reply-To: <20190119011314.45cb9864@naga> References: <20190117121328.13395-1-mpe@ellerman.id.au> <20190117121328.13395-4-mpe@ellerman.id.au> <20190119011314.45cb9864@naga> Date: Sat, 19 Jan 2019 21:27:21 +1100 Message-ID: <87won12b92.fsf@concordia.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable 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" Michal Such=C3=A1nek writes: > On Thu, 17 Jan 2019 23:13:28 +1100 > Michael Ellerman wrote: > >> On machines with 1TB segments and a 32-entry SLB it's quite hard to >> cause sufficient SLB pressure to trigger bugs caused due to badly >> timed SLB faults. >>=20 >> We have seen this in the past and a few years ago added the >> disable_1tb_segments command line option to force the use of 256MB >> segments. However even this allows some bugs to slip through testing >> if the SLB entry in question was recently accessed. >>=20 >> So add a new command line parameter for debugging which shrinks the >> SLB to the minimum size we can support. Currently that size is 3, two >> bolted SLBs and 1 for dynamic use. This creates the maximal SLB > > Doesn't this violate the power of 2 requirement stated in 2/4? Yes. Good point. This was originally a hack patch in my tree, back when SLB_NUM_BOLTED was 3 and before Nick even added the slb_used_bitmap, so back then it was a power of 2 but it also didn't matter :) I think I'll rework the slb_full_bitmap patch anyway and remove the power of 2 requirement, so then this patch will be OK. Thanks for the review! cheers