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Wed, 28 Apr 2021 09:31:34 +0000 (GMT) Received: from oc7455500831.ibm.com (unknown [9.171.77.184]) by b06wcsmtp001.portsmouth.uk.ibm.com (Postfix) with ESMTP; Wed, 28 Apr 2021 09:31:34 +0000 (GMT) Subject: Re: sched: Move SCHED_DEBUG sysctl to debugfs To: Peter Zijlstra Cc: bristot@redhat.com, bsegall@google.com, dietmar.eggemann@arm.com, greg@kroah.com, gregkh@linuxfoundation.org, joshdon@google.com, juri.lelli@redhat.com, linux-kernel@vger.kernel.org, linux@rasmusvillemoes.dk, mgorman@suse.de, mingo@kernel.org, rostedt@goodmis.org, valentin.schneider@arm.com, vincent.guittot@linaro.org, linux-s390@vger.kernel.org, kvm@vger.kernel.org References: <20210412102001.287610138@infradead.org> <20210427145925.5246-1-borntraeger@de.ibm.com> From: Christian Borntraeger Message-ID: <2326ce94-3707-b099-4fe8-c79547bd8e25@de.ibm.com> Date: Wed, 28 Apr 2021 11:31:34 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.9.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: rcj_GYXrVcyKoaoaSbUMxbF98QFld4ox X-Proofpoint-GUID: XAA5ieffU6naM4zQX3nA2hP0P-aUZIKs X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.391,18.0.761 definitions=2021-04-28_03:2021-04-27,2021-04-28 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 adultscore=0 priorityscore=1501 phishscore=0 impostorscore=0 malwarescore=0 lowpriorityscore=0 clxscore=1015 bulkscore=0 mlxscore=0 spamscore=0 mlxlogscore=992 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2104060000 definitions=main-2104280062 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 28.04.21 11:25, Peter Zijlstra wrote: > On Wed, Apr 28, 2021 at 10:54:37AM +0200, Christian Borntraeger wrote: >> >> >> On 28.04.21 10:46, Peter Zijlstra wrote: >>> On Tue, Apr 27, 2021 at 04:59:25PM +0200, Christian Borntraeger wrote: >>>> Peter, >>>> >>>> I just realized that we moved away sysctl tunabled to debugfs in next. >>>> We have seen several cases where it was benefitial to set >>>> sched_migration_cost_ns to a lower value. For example with KVM I can >>>> easily get 50% more transactions with 50000 instead of 500000. >>>> Until now it was possible to use tuned or /etc/sysctl.conf to set >>>> these things permanently. >>>> >>>> Given that some people do not want to have debugfs mounted all the time >>>> I would consider this a regression. The sysctl tunable was always >>>> available. >>>> >>>> I am ok with the "informational" things being in debugfs, but not >>>> the tunables. So how do we proceed here? >>> >>> It's all SCHED_DEBUG; IOW you're relying on DEBUG infrastructure for >>> production performance, and that's your fail. >> >> No its not. sched_migration_cost_ns was NEVER protected by CONFIG_SCHED_DEBUG. >> It was available on all kernels with CONFIG_SMP. > > The relevant section from origin/master:kernel/sysctl.c: [...] > How is migration_cost not under SCHED_DEBUG? The bigger problem is that > world+dog has SCHED_DEBUG=y in their .config. Hmm, yes my bad. I disabled it but it was silently reenabled due to a dependency. So yes you are right, it is under SCHED_DEBUG.