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

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

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


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