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Thu, 21 Sep 2023 15:45:27 +0000 (GMT) MIME-Version: 1.0 Date: Thu, 21 Sep 2023 10:45:26 -0500 From: Glenn Miles To: Nicholas Piggin Cc: qemu-devel@nongnu.org, Daniel Henrique Barboza , =?UTF-8?Q?C=C3=A9dric_Le_Goater?= , David Gibson , Greg Kurz , "open list:PowerPC TCG CPUs" Subject: Re: [PATCH 2/4] target/ppc: Add recording of taken branches to BHRB In-Reply-To: <955aa084c1e56559943f17514d7bed73@linux.vnet.ibm.com> References: <20230912192144.3330174-1-milesg@linux.vnet.ibm.com> <20230912202421.3381779-1-milesg@linux.vnet.ibm.com> <955aa084c1e56559943f17514d7bed73@linux.vnet.ibm.com> Message-ID: X-Sender: milesg@linux.vnet.ibm.com Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: qYGoJQHfjU3KzlMRJ9er6gIbl9HPT25L X-Proofpoint-GUID: NOAzsx5p75DeIEQSfD6Zv2ft_R2iP9sF X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.267,Aquarius:18.0.980,Hydra:6.0.619,FMLib:17.11.176.26 definitions=2023-09-21_13,2023-09-21_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 bulkscore=0 priorityscore=1501 impostorscore=0 mlxlogscore=475 suspectscore=0 clxscore=1015 adultscore=0 malwarescore=0 mlxscore=0 spamscore=0 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2308100000 definitions=main-2309210134 Received-SPF: none client-ip=148.163.158.5; envelope-from=milesg@linux.vnet.ibm.com; helo=mx0b-001b2d01.pphosted.com X-Spam_score_int: -19 X-Spam_score: -2.0 X-Spam_bar: -- X-Spam_report: (-2.0 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_NONE=0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org >> It all looks pretty good otherwise. I do worry about POWER8/9 which >> do not have BHRB disable bit. How much do they slow down I wonder? > > That is a good question! I'll see if I can get some linux boot times > with and without the changes on P9. > I ran some tests booting ubuntu 20.04 on the powrnv9 model and found that it took about 5% longer to boot to the login prompt with the changes than without. As discussed offline, I'll remove this support from P8/P9 as the 5% reduction in performance is not worth the added functionality. We could perhaps add it back in the future with a command line option that has it disabled by default on P8/P9. P10 and on has it disabled for non problem state branches, so we should be good there. Thanks, Glenn