Re: [PATCH] x86/fred: Optimize the FRED entry by prioritizing high-probability event dispatching

[H. Peter Anvin]

On 1/16/25 16:37, Ethan Zhao wrote:
> > hpa suggested to introduce "switch_likely" for this kind of optimization
> > on a switch statement, which is also easier to read.  I measured it with
> > a user space focus test, it does improve performance a lot.  But 
> > obviously there are still a lot of work to do.
>
> Find a way to instruct compiler to pick the right hot branch meanwhile 
> make folks
> reading happy... yup, a lot of work.

It's not that complicated, believe it or not.

/*
 * switch(v) biased for speed in the case v == l
 *
 * Note: gcc is quite sensitive to the exact form of this
 * expression.
 */
#define switch_likely(v,l) \
	switch((__typeof__(v))__builtin_expect((v),(l)))

	-hpa