Re: [PATCH 3 of 3] xen: sched_credit: add some tracing

[George Dunlap <george.dunlap@eu.citrix.com>]

On 05/12/12 12:20, Ian Campbell wrote:
> On Wed, 2012-12-05 at 12:15 +0000, Dario Faggioli wrote:
>> On Wed, 2012-12-05 at 12:01 +0000, Ian Campbell wrote:
>>>> As I tried to explain in the comment, I just wanted to avoid checking
>>>> for !tb_init_done more than once, as this happens within a loop and, at
>>>> least potentially, there may be more CPUs to tickle (and thus more calls
>>>> to TRACE_1D).
>>> If tb_init_done isn't marked volatile or anything like that isn't the
>>> check hoisted out of the loop by the compiler?
>>>
>> Good point. As they're all macros, yes, I think that is something very
>> likely to happen... Although, I haven't checked the generated code, I'll
>> take a look. Thanks.
>>
>>>> I take this comment of yours as you not thinking that is
>>>> something worthwhile, right? If so, I can definitely turn this into a
>>>> "standard" TRACE_1D() call.
>>> Or maybe consider __TRACE_1D and friends which omit the check?
>>>
>> Mmm... It may well be me, but my
>>
>> $ grep __TRACE xen/* -R
>>
>> does not show any results... What am I missing?
> I meant to define + use those macros.

Well ATM there would be only one user -- and "trace_var(..., 
sizeof(cpu), &cpu);" is probably just as pretty as __TRACE_1D(..., cpu).

I wouldn't oppose such a patch, but I don't think it should be required 
until we want to use "__TRACE_(N>2)D".

  -George