From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Hildenbrand Subject: Re: [PATCH/RFC] KVM: halt_polling: provide a way to qualify wakeups during poll Date: Mon, 2 May 2016 12:45:48 +0200 Message-ID: <20160502124548.1a80cf32@thinkpad-w530> References: <1462185753-14634-1-git-send-email-borntraeger@de.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: Paolo Bonzini , Radim =?UTF-8?B?S3LEjW3DocWZ?= , KVM , Cornelia Huck , linux-s390 , Jens Freimann To: Christian Borntraeger Return-path: Received: from e06smtp06.uk.ibm.com ([195.75.94.102]:53343 "EHLO e06smtp06.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753665AbcEBKp5 (ORCPT ); Mon, 2 May 2016 06:45:57 -0400 Received: from localhost by e06smtp06.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 2 May 2016 11:45:55 +0100 In-Reply-To: <1462185753-14634-1-git-send-email-borntraeger@de.ibm.com> Sender: kvm-owner@vger.kernel.org List-ID: > Radim, Paolo, > > can you have a look at this patch? If you are ok with it, I want to > submit this patch with my next s390 pull request. It touches KVM common > code, but I tried to make it a nop for everything but s390. > > Christian > > ----snip---- > > > Some wakeups should not be considered a sucessful poll. For example on > s390 I/O interrupts are usually floating, which means that _ALL_ CPUs > would be considered runnable - letting all vCPUs poll all the time for > transactional like workload, even if one vCPU would be enough. > This can result in huge CPU usage for large guests. > This patch lets architectures provide a way to qualify wakeups if they > should be considered a good/bad wakeups in regard to polls. > > For s390 the implementation will fence of halt polling for anything but > known good, single vCPU events. The s390 implementation for floating > interrupts does a wakeup for one vCPU, but the interrupt will be delivered > by whatever CPU comes first. To limit the halt polling we only mark the > woken up CPU as a valid poll. This code will also cover several other > wakeup reasons like IPI or expired timers. This will of course also mark > some events as not sucessful. As KVM on z runs always as a 2nd level > hypervisor, we prefer to not poll, unless we are really sure, though. > > So we start with a minimal set and will provide additional patches in > the future that mark additional code paths as valid wakeups, if that > turns out to be necessary. > > This patch successfully limits the CPU usage for cases like uperf 1byte > transactional ping pong workload or wakeup heavy workload like OLTP > while still providing a proper speedup. > > Signed-off-by: Christian Borntraeger > --- > arch/s390/kvm/Kconfig | 1 + > arch/s390/kvm/interrupt.c | 8 ++++++++ > include/linux/kvm_host.h | 34 ++++++++++++++++++++++++++++++++++ > virt/kvm/Kconfig | 4 ++++ > virt/kvm/kvm_main.c | 9 ++++++--- > 5 files changed, 53 insertions(+), 3 deletions(-) > Acked-by: David Hildenbrand David