From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: [PATCH] KVM: x86: Convert tsc_write_lock to raw_spinlock Date: Tue, 08 Feb 2011 10:55:51 +0100 Message-ID: <4D511327.1020102@siemens.com> References: <4D4BCB97.6000900@siemens.com> <4D4C698A.4010201@redhat.com> <4D4FD8EE.6040009@siemens.com> <4D4FFD97.6010805@redhat.com> <4D5008F0.5060200@siemens.com> <4D500C9F.2080501@redhat.com> <4D50120F.4030809@siemens.com> <4D501547.6040907@redhat.com> <4D501698.1000507@siemens.com> <4D501D43.5060608@redhat.com> <4D5024F3.9090105@siemens.com> <4D5027A1.8000505@redhat.com> <4D502AA5.7040407@siemens.com> <4D5109CC.2030901@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Cc: Zachary Amsden , Marcelo Tosatti , kvm , Linux Kernel Mailing List To: Avi Kivity Return-path: In-Reply-To: <4D5109CC.2030901@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 2011-02-08 10:15, Avi Kivity wrote: > On 02/07/2011 07:23 PM, Jan Kiszka wrote: >> On 2011-02-07 18:10, Avi Kivity wrote: >>> On 02/07/2011 06:59 PM, Jan Kiszka wrote: >>>>> >>>>> (well, actually, cpufreq_notifier and kvm_arch_hardware_enable are >>>>> already non preemptible, and the stats code should just go away?) >>>> >>>> The stats code is trivial to convert, so it doesn't matter. >>> >>> Removal is easier. >> >> Is that stat interface no longer used? > > It's there for compatibility. I'm itching to remove it. See > qemu-kvm.git/kvm/kvm_stat for the only known user, and for the > replacement via tracepoints. OK, but that will first take a grace period. > > Tracepoints have marginally lower overhead when disabled, and somewhat > higher overhead when enabled. A disadvantage of tracepoints is that it > is harder to associate an event with a vm when that event is triggered > by a workqueue, but I don't think it matters in practice (kvm_stat > doesn't even provide a per-vm breakdown). What about using the perf infrastructure for this? Besides that perf can reuse tracepoints, maybe there is even a more efficient way of added new stat sources. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux