Re: [Xen-devel] [RFC][PATCH] eliminate extra tb_init_done check

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 15/10/08 07:20, "Lu, Guanqun" <guanqun.lu@xxxxxxxxx> wrote:

> Two corner conditions are left untouched. One is the assembly in entry.S,
> the other is the check of tb_init_done not immediately followed by
> __trace_var.
> 
> Or more aggressively, we can eliminate all the extra checks, make tb_init_done
> a static variable, and rename __trace_var to trace_var which looks more like
> a right interface name.

The macros check tb_init_done before calling __trace_var() to try and reduce
the cost of the common case (tracing disabled) as far as possible. Hence we
avoid a function call and computation of some arguments to that function.

I don't know if we've actually measured teh performance win from this. If we
have, George would know about it.

 -- Keir



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