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    SubjectRe: [PATCH 07/15] ftrace: fix event alignment: kvm:kvm_hv_hypercall
    On Sat, Dec 4, 2010 at 12:11 AM, Avi Kivity <avi@redhat.com> wrote:
    > On 12/04/2010 02:13 AM, David Sharp wrote:
    >>
    >> Signed-off-by: David Sharp<dhsharp@google.com>
    >> ---
    >>  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 have a truly marvellous patch that fixes the bug which this
    > signature is too narrow to contain.
    >
    >
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