From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christian Borntraeger Subject: Re: [4.2] commit d59cfc09c32 (sched, cgroup: replace signal_struct->group_rwsem with a global percpu_rwsem) causes regression for libvirt/kvm Date: Wed, 16 Sep 2015 10:57:40 +0200 Message-ID: <55F92F04.1040706@de.ibm.com> References: <55F8097A.7000206@de.ibm.com> <20150915130550.GC16853@twins.programming.kicks-ass.net> <55F81EE2.4090708@de.ibm.com> <55F84A6B.1010207@redhat.com> <20150915173836.GO4029@linux.vnet.ibm.com> <55F92904.4090206@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Cc: Peter Zijlstra , Tejun Heo , Ingo Molnar , "linux-kernel@vger.kernel.org >> Linux Kernel Mailing List" , KVM list , Oleg Nesterov To: Paolo Bonzini , paulmck@linux.vnet.ibm.com Return-path: Received: from e06smtp07.uk.ibm.com ([195.75.94.103]:45100 "EHLO e06smtp07.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752110AbbIPI5t (ORCPT ); Wed, 16 Sep 2015 04:57:49 -0400 Received: from /spool/local by e06smtp07.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 16 Sep 2015 09:57:45 +0100 In-Reply-To: <55F92904.4090206@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: Am 16.09.2015 um 10:32 schrieb Paolo Bonzini: > > > On 15/09/2015 19:38, Paul E. McKenney wrote: >> Excellent points! >> >> Other options in such situations include the following: >> >> o Rework so that the code uses call_rcu*() instead of *_expedited(). >> >> o Maintain a per-task or per-CPU counter so that every so many >> *_expedited() invocations instead uses the non-expedited >> counterpart. (For example, synchronize_rcu instead of >> synchronize_rcu_expedited().) > > Or just use ratelimit (untested): One of my tests was to always replace synchronize_sched_expedited with synchronize_sched and things turned out to be even worse. Not sure if it makes sense to test yopur in-the-middle approach? Christian