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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 568BECDB465 for ; Thu, 19 Oct 2023 11:51:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233171AbjJSLu7 (ORCPT ); Thu, 19 Oct 2023 07:50:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60226 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232977AbjJSLu4 (ORCPT ); Thu, 19 Oct 2023 07:50:56 -0400 Received: from gandalf.ozlabs.org (mail.ozlabs.org [IPv6:2404:9400:2221:ea00::3]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C34C8BE for ; Thu, 19 Oct 2023 04:50:54 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ellerman.id.au; s=201909; t=1697716249; bh=QVNmT0LMj8mt5yv4FZ1LFFQtgL5o7wdHisErTaVs4hE=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=Rmar2YgEngG8pbe1XRhd/jpc3FiE/6WmFa6NDuRcLlK6yAxHuJMH6qD9lDSfW+6az 3wWovzJWSHUNxe5sHAgGmOT7F7cZuePWOnfokLxsY1ulLzAzVBPjEFMECw4Gr0ETwZ 1YZ+aboGXQFo+H+gnshFjMoIqfZvlNiezc8WFyFrDnHNlkNlhBb2OoPS7AfRacnTkC EDBqTflVoGwLTRmbNUZvlk7eA3PX/PAuTHG5Ke4fwRxANfX/nr2KMKjmbQZSbvLstA w7axDAUvC56hYILjiXhau9N65HeHs/V7qlBFnwopA+nPzAWUB9wgnYbKg9wfy07EcJ Ao+1wEY0JMulw== 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 X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by mail.ozlabs.org (Postfix) with ESMTPSA id 4SB5dM5p59z4xZm; Thu, 19 Oct 2023 22:50:47 +1100 (AEDT) From: Michael Ellerman To: Peter Zijlstra Cc: Srikar Dronamraju , linuxppc-dev , Christophe Leroy , Nicholas Piggin , Rohan McLure , Valentin Schneider , Josh Poimboeuf , Mark Rutland , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 2/6] powerpc/smp: Enable Asym packing for cores on shared processor In-Reply-To: <20231019074828.GM33217@noisy.programming.kicks-ass.net> References: <20231018163751.2423181-1-srikar@linux.vnet.ibm.com> <20231018163751.2423181-3-srikar@linux.vnet.ibm.com> <87v8b35ir3.fsf@mail.lhotse> <20231019074828.GM33217@noisy.programming.kicks-ass.net> Date: Thu, 19 Oct 2023 22:50:43 +1100 Message-ID: <87h6mm6dbg.fsf@mail.lhotse> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Peter Zijlstra writes: > On Thu, Oct 19, 2023 at 03:38:40PM +1100, Michael Ellerman wrote: >> Srikar Dronamraju writes: >> > If there are shared processor LPARs, underlying Hypervisor can have more >> > virtual cores to handle than actual physical cores. >> > >> > Starting with Power 9, a core has 2 nearly independent thread groups. >> >> You need to be clearer here that you're talking about "big cores", not >> SMT4 cores as seen on bare metal systems. > > What is a 'big core' ? I'm thinking big.LITTLE, but I didn't think Power > went that route (yet?).. help? No it's not big.LITTLE :) It means we have two SMT4 cores glued together that behave as a single SMT8 core, a system is either in "big core" mode or it's not, it's never heterogeneous. If you grep for "big_core" there's some code in the kernel for dealing with it, though it's probably not very illuminating. Possibly we should switch to using the "thread group" terminology, so that it doesn't confuse folks about big.LITTLE. Also the device tree property that we use to discover if we're using big cores is called ibm,thread-groups. cheers