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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2012-12-05 at 11:54 +0000, Dario Faggioli wrote:
> On Tue, 2012-12-04 at 19:10 +0000, George Dunlap wrote: 
> > On 03/12/12 16:35, Dario Faggioli wrote:
> > > +            /* Avoid TRACE_* to avoid a lot of useless !tb_init_done 
> > > checks */
> > > +            for_each_cpu(cpu, &mask)
> > > +            {
> > > +                struct {
> > > +                    unsigned cpu:8;
> > > +                } d;
> > > +                d.cpu = cpu;
> > > +                trace_var(TRC_CSCHED_TICKLE, 0,
> > > +                          sizeof(d),
> > > +                          (unsigned char*)&d);
> > 
> > Why not just TRC_1D()? 
> >
> 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?

> 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?

Ian.


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