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Mon, 29 Jun 2020 10:42:55 +0000 (GMT) Received: from b03ledav003.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 7DC9E6A058; Mon, 29 Jun 2020 10:42:54 +0000 (GMT) Received: from sofia.ibm.com (unknown [9.85.80.55]) by b03ledav003.gho.boulder.ibm.com (Postfix) with ESMTP; Mon, 29 Jun 2020 10:42:54 +0000 (GMT) Received: by sofia.ibm.com (Postfix, from userid 1000) id 046E32E4AC7; Mon, 29 Jun 2020 16:12:48 +0530 (IST) Date: Mon, 29 Jun 2020 16:12:48 +0530 From: Gautham R Shenoy To: Joel Stanley Subject: Re: [PATCH] powerpc: Warn about use of smt_snooze_delay Message-ID: <20200629104248.GD20062@in.ibm.com> References: <20200625100349.2408899-1-joel@jms.id.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200625100349.2408899-1-joel@jms.id.au> User-Agent: Mutt/1.5.23 (2014-03-12) X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.216, 18.0.687 definitions=2020-06-29_08:2020-06-29, 2020-06-29 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 suspectscore=0 cotscore=-2147483648 mlxscore=0 bulkscore=0 mlxlogscore=999 adultscore=0 malwarescore=0 priorityscore=1501 impostorscore=0 phishscore=0 spamscore=0 clxscore=1011 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2006290071 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: ego@linux.vnet.ibm.com Cc: linuxppc-dev@lists.ozlabs.org, ego@linux.ibm.com Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Thu, Jun 25, 2020 at 07:33:49PM +0930, Joel Stanley wrote: > It's not done anything for a long time. Save the percpu variable, and > emit a warning to remind users to not expect it to do anything. > > Signed-off-by: Joel Stanley The only known user of "smt_snooze_delay" is the "ppc64_cpu" which uses the presence of this file to assume that the system is SMT capable. Since we have "/sys/devices/system/cpu/smt/" these days, perhaps the userspace utility can use that and we can get rid of the file altogether ? FWIW, Acked-by: Gautham R. Shenoy > --- > arch/powerpc/kernel/sysfs.c | 41 +++++++++++++------------------------ > 1 file changed, 14 insertions(+), 27 deletions(-) > > diff --git a/arch/powerpc/kernel/sysfs.c b/arch/powerpc/kernel/sysfs.c > index 571b3259697e..530ae92bc46d 100644 > --- a/arch/powerpc/kernel/sysfs.c > +++ b/arch/powerpc/kernel/sysfs.c > @@ -32,29 +32,25 @@ > > static DEFINE_PER_CPU(struct cpu, cpu_devices); > > -/* > - * SMT snooze delay stuff, 64-bit only for now > - */ > - > #ifdef CONFIG_PPC64 > > -/* Time in microseconds we delay before sleeping in the idle loop */ > -static DEFINE_PER_CPU(long, smt_snooze_delay) = { 100 }; > +/* > + * Snooze delay has not been hooked up since 3fa8cad82b94 ("powerpc/pseries/cpuidle: > + * smt-snooze-delay cleanup.") and has been broken even longer. As was foretold in > + * 2014: > + * > + * "ppc64_util currently utilises it. Once we fix ppc64_util, propose to clean > + * up the kernel code." > + * > + * At some point in the future this code should be removed. > + */ > > static ssize_t store_smt_snooze_delay(struct device *dev, > struct device_attribute *attr, > const char *buf, > size_t count) > { > - struct cpu *cpu = container_of(dev, struct cpu, dev); > - ssize_t ret; > - long snooze; > - > - ret = sscanf(buf, "%ld", &snooze); > - if (ret != 1) > - return -EINVAL; > - > - per_cpu(smt_snooze_delay, cpu->dev.id) = snooze; > + WARN_ON_ONCE("smt_snooze_delay sysfs file has no effect\n"); > return count; > } > > @@ -62,9 +58,9 @@ static ssize_t show_smt_snooze_delay(struct device *dev, > struct device_attribute *attr, > char *buf) > { > - struct cpu *cpu = container_of(dev, struct cpu, dev); > + WARN_ON_ONCE("smt_snooze_delay sysfs file has no effect\n"); > > - return sprintf(buf, "%ld\n", per_cpu(smt_snooze_delay, cpu->dev.id)); > + return sprintf(buf, "100\n"); > } > > static DEVICE_ATTR(smt_snooze_delay, 0644, show_smt_snooze_delay, > @@ -72,16 +68,7 @@ static DEVICE_ATTR(smt_snooze_delay, 0644, show_smt_snooze_delay, > > static int __init setup_smt_snooze_delay(char *str) > { > - unsigned int cpu; > - long snooze; > - > - if (!cpu_has_feature(CPU_FTR_SMT)) > - return 1; > - > - snooze = simple_strtol(str, NULL, 10); > - for_each_possible_cpu(cpu) > - per_cpu(smt_snooze_delay, cpu) = snooze; > - > + WARN_ON_ONCE("smt-snooze-delay command line option has no effect\n"); > return 1; > } > __setup("smt-snooze-delay=", setup_smt_snooze_delay); > -- > 2.27.0 >