Re: [PATCH 07/15] ftrace: fix event alignment: kvm:kvm_hv_hypercall

[David Sharp]

On Sat, Dec 4, 2010 at 12:11 AM, Avi Kivity <avi@xxxxxxxxxx> wrote:
> On 12/04/2010 02:13 AM, David Sharp wrote:
>>
>> Signed-off-by: David Sharp<dhsharp@xxxxxxxxxx>
>> ---
>> Âarch/x86/kvm/trace.h | Â Â8 ++++----
>> Â1 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,
>> Â Â Â ÂTP_ARGS(code, fast, rep_cnt, rep_idx, ingpa, outgpa),
>>
>> Â Â Â ÂTP_STRUCT__entry(
>> -        __field(    Â__u16,     Âcode      Â)
>> -        __field(    Âbool,      fast      Â)
>>        Â__field(    Â__u16,     Ârep_cnt     )
>>        Â__field(    Â__u16,     Ârep_idx     )
>>        Â__field(    Â__u64,     Âingpa      )
>>        Â__field(    Â__u64,     Âoutgpa     Â)
>> +        __field(    Â__u16,     Âcode      Â)
>> +        __field(    Âbool,      fast      Â)
>> Â Â Â Â),
>>
>
> 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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