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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Mon, 15 Apr 2019 10:42:56 +0100 Received: from d06av26.portsmouth.uk.ibm.com (d06av26.portsmouth.uk.ibm.com [9.149.105.62]) by b06cxnps3075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x3F9gtQq48627726 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 15 Apr 2019 09:42:55 GMT Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 58E00AE051; Mon, 15 Apr 2019 09:42:55 +0000 (GMT) Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 086F9AE057; Mon, 15 Apr 2019 09:42:55 +0000 (GMT) Received: from localhost (unknown [9.124.35.82]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTP; Mon, 15 Apr 2019 09:42:54 +0000 (GMT) Date: Mon, 15 Apr 2019 15:12:53 +0530 From: "Naveen N. Rao" Subject: Re: [RFC PATCH] powerpc/64/ftrace: mprofile-kernel patch out mflr To: linuxppc-dev@lists.ozlabs.org, Nicholas Piggin References: <20190413015940.31170-1-npiggin@gmail.com> In-Reply-To: <20190413015940.31170-1-npiggin@gmail.com> User-Agent: astroid/0.14.0 (https://github.com/astroidmail/astroid) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable X-TM-AS-GCONF: 00 x-cbid: 19041509-0020-0000-0000-0000032FE8CF X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19041509-0021-0000-0000-00002182271B Message-Id: <1555321078.e0y6xbi5qm.naveen@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:, , definitions=2019-04-15_04:, , signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=595 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1904150068 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: , Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Hi Nick, Nicholas Piggin wrote: > The new mprofile-kernel mcount sequence is >=20 > mflr r0 > bl _mcount >=20 > Dynamic ftrace patches the branch instruction with a noop, but leaves > the mflr. mflr is executed by the branch unit that can only execute one > per cycle on POWER9 and shared with branches, so it would be nice to > avoid it where possible. >=20 > This patch is a hacky proof of concept to nop out the mflr. Can we do > this or are there races or other issues with it? Thanks for implementing this. I don't see a problem with this. - Naveen =