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Fri, 31 Jul 2020 09:29:06 +0000 Received: from d06av23.portsmouth.uk.ibm.com (d06av23.portsmouth.uk.ibm.com [9.149.105.59]) by b06cxnps4076.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 06V9T4ta58130526 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 31 Jul 2020 09:29:04 GMT Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id B4AFAA4040; Fri, 31 Jul 2020 09:29:04 +0000 (GMT) Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 768DBA404D; Fri, 31 Jul 2020 09:29:02 +0000 (GMT) Received: from linux.vnet.ibm.com (unknown [9.126.150.29]) by d06av23.portsmouth.uk.ibm.com (Postfix) with SMTP; Fri, 31 Jul 2020 09:29:02 +0000 (GMT) Date: Fri, 31 Jul 2020 14:59:01 +0530 From: Srikar Dronamraju To: Michael Ellerman Subject: Re: [PATCH v4 06/10] powerpc/smp: Generalize 2nd sched domain Message-ID: <20200731092901.GH14603@linux.vnet.ibm.com> References: <20200727053230.19753-1-srikar@linux.vnet.ibm.com> <20200727053230.19753-7-srikar@linux.vnet.ibm.com> <875za45dr2.fsf@mpe.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <875za45dr2.fsf@mpe.ellerman.id.au> User-Agent: Mutt/1.10.1 (2018-07-13) X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235, 18.0.687 definitions=2020-07-31_02:2020-07-31, 2020-07-31 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 clxscore=1015 suspectscore=0 adultscore=0 mlxscore=0 lowpriorityscore=0 bulkscore=0 malwarescore=0 mlxlogscore=999 priorityscore=1501 impostorscore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2007310068 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: , Reply-To: Srikar Dronamraju Cc: Nathan Lynch , Gautham R Shenoy , Michael Neuling , Peter Zijlstra , Jordan Niethe , LKML , Nicholas Piggin , Valentin Schneider , Oliver O'Halloran , linuxppc-dev , Ingo Molnar Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" * Michael Ellerman [2020-07-31 17:45:37]: > Srikar Dronamraju writes: > > Currently "CACHE" domain happens to be the 2nd sched domain as per > > powerpc_topology. This domain will collapse if cpumask of l2-cache is > > same as SMT domain. However we could generalize this domain such that it > > could mean either be a "CACHE" domain or a "BIGCORE" domain. > > > > While setting up the "CACHE" domain, check if shared_cache is already > > set. > > PeterZ asked for some overview of what you're doing and why, you > responded to his mail, but I was expecting to see that text incorporated > here somewhere. > Okay, do you want that as part of the code or documentation dir or the changelog? > He also asked for some comments, which I would also like to see. > > > I'm also not clear why we want to rename it to "bigcore", that's not a > commonly understood term, I don't think it's clear to new readers what > it means. > > Leaving it as the shared cache domain, and having a comment mentioning > that "bigcores" share a cache, would be clearer I think. > Today, Shared cache is equal to Big Core. However in not too distant future, Shared cache domain and Big Core may not be the same. For example lets assume that L2 cache were to Shrink per small core with the firmware exposing the core as a bigcore. Then with the current design, we have a SMT == SHARED CACHE, and a DIE. We would not have any domain at the publicised 8 thread level. Keeping the Bigcore as a domain and mapping the shared cache, (I am resetting the domain name as CACHE if BIGCORE==SHARED_CACHE), helps us in this scenario. > cheers > -- Thanks and Regards Srikar Dronamraju