From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [patch 0/4] Port KVM-trace to tracepoints Date: Tue, 22 Jul 2008 22:31:51 +0300 Message-ID: <488635A7.2030609@qumranet.com> References: <20080717155724.897537670@polymtl.ca> <48862A30.7050701@qumranet.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Mathieu Desnoyers , akpm@linux-foundation.org, Ingo Molnar , linux-kernel@vger.kernel.org, Peter Zijlstra , kvm@vger.kernel.org To: "Frank Ch. Eigler" Return-path: Received: from il.qumranet.com ([212.179.150.194]:14232 "EHLO il.qumranet.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756727AbYGVTbz (ORCPT ); Tue, 22 Jul 2008 15:31:55 -0400 In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: Frank Ch. Eigler wrote: > Avi Kivity writes: > > >> [...] >> kvm tracepoints are heavily tied into the implementation; and making >> them harder to write means we will have less information. In fact, I >> am contemplating moving in another direction (when looking at the >> pgprintk()s scattered around arch/x86/kvm/mmu.c: >> >> kvm_trace("pfentry", "page_fault entry addr %lx error code %x\n", >> cr2, error_code); >> >> Unlike printk()s, no actual formatting would occur during runtime. >> > > Have you considered using trace_mark() directly - eliminating the > KVM_TRACEN() middlemen? > > Eliminating KVM_TRACEN -- yes. There are too many of them, they aren't type-aware, and they're in uppercase. Using trace_mark() directly -- looking at it, seems to fit the requirements exactly. Should have looked at it earlier. Is there a way to get a list of all markers? Perhaps the kvmtrace marker->relay integration should be made a marker feature, since there is nothing specific to kvm in it. >> Instead, at initialization time all the strings would be parsed into >> a data structure that describes the data types, and the runtime >> would simply consult this structure and copy the arguments into >> trace records. User space would also be able to pull this structure >> and so recreate the formatted string. >> > > If one really wanted to, one could build such a mechanism on top of > marker-based callbacks. > > One does want to. >> - no need to have a formats file in userspace (which is tied to the >> kernel version) >> > > OTOH, you'd have the kernel collecting compact binary records > containing just the parameters, which are at least as tied to kernel > version. > > Yes, but the userspace side would collect the format strings as well (just once) and could put them in the same file. The aggregation is portable across kernel versions. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.