Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754917Ab0LGJXG (ORCPT ); Tue, 7 Dec 2010 04:23:06 -0500 Received: from mx1.redhat.com ([209.132.183.28]:57224 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752444Ab0LGJXD (ORCPT ); Tue, 7 Dec 2010 04:23:03 -0500 Message-ID: <4CFDFCEF.3080708@redhat.com> Date: Tue, 07 Dec 2010 11:22:55 +0200 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.12) Gecko/20101103 Fedora/1.0-0.33.b2pre.fc14 Lightning/1.0b3pre Thunderbird/3.1.6 MIME-Version: 1.0 To: David Sharp CC: rostedt@goodmis.org, linux-kernel@vger.kernel.org, mrubin@google.com, kvm-devel Subject: Re: [PATCH 07/15] ftrace: fix event alignment: kvm:kvm_hv_hypercall References: <1291421609-14665-1-git-send-email-dhsharp@google.com> <1291421609-14665-8-git-send-email-dhsharp@google.com> <4CF9F7AB.8050802@redhat.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2079 Lines: 51 On 12/06/2010 10:38 PM, David Sharp wrote: > On Sat, Dec 4, 2010 at 12:11 AM, Avi Kivity wrote: > > On 12/04/2010 02:13 AM, David Sharp wrote: > >> > >> Signed-off-by: David Sharp > >> --- > >> arch/x86/kvm/trace.h | 8 ++++---- > >> 1 files changed, 4 insertions(+), 4 deletions(-) > >> > >> diff --git a/arch/x86/kvm/trace.h b/arch/x86/kvm/trace.h > >> index a6544b8..ab41fb0 100644 > >> --- a/arch/x86/kvm/trace.h > >> +++ b/arch/x86/kvm/trace.h > >> @@ -62,21 +62,21 @@ TRACE_EVENT(kvm_hv_hypercall, > >> TP_ARGS(code, fast, rep_cnt, rep_idx, ingpa, outgpa), > >> > >> TP_STRUCT__entry( > >> - __field( __u16, code ) > >> - __field( bool, fast ) > >> __field( __u16, rep_cnt ) > >> __field( __u16, rep_idx ) > >> __field( __u64, ingpa ) > >> __field( __u64, outgpa ) > >> + __field( __u16, code ) > >> + __field( bool, fast ) > >> ), > >> > > > > Looks like a pessimisation. > > > > Before: 24 bytes > > After: 32 bytes > > > > (on a 64-bit machine, assuming no packing) > > This patch is predicated on packing the event structures. And since > the ring buffer is 32-bit addressable, I don't attempt to improve > alignment beyond 32-bit boundaries. I don't understand this. Can you elaborate? What does "32-bit addressable" mean? And "predicated on packing the event structures"? Is the structure __attribute__((packed)), or is it not? -- error compiling committee.c: too many arguments to function -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/