RE: [PATCH v7 1/6] riscv: mm: dma-noncoherent: Switch using function pointers for cache management

Biju Das <biju.das.jz@xxxxxxxxxxxxxx> · Wed, 5 Apr 2023 06:08:27 +0000

Hi Christoph Hellwig,

Thanks for the feedback.

> Subject: Re: [PATCH v7 1/6] riscv: mm: dma-noncoherent: Switch using
> function pointers for cache management
> 
> On Tue, Apr 04, 2023 at 06:24:16AM +0000, Biju Das wrote:
> > Just a question, how does function pointer makes a performance
> > difference compared to
> > ALTERNATIVE_X() macros?
> >
> > On both cases, we are pushing function parameters to stack, jumping to
> > the actual routine And then on return pop the variables from stack. Am I
> missing something here?
> 
> Indirect calls have always been more expensive, and with the hard- and
> software mitigations for spectre-like attacks they are becoming even more
> expensive.

Thanks for the info. I agree, it will be more expensive with software mitigations
for spectre-like attacks.

Cheers,
Biju