Re: [PATCH v2 17/26] selftests/resctrl: Replace file write with volatile variable

Reinette Chatre
2023-11-28T22:16:47Z

Hi Ilpo,

On 11/20/2023 3:13 AM, Ilpo Järvinen wrote:
> The fill_buf code prevents compiler optimizating the entire read loop
> away by writing the final value of the variable into a file. While it
> achieves the goal, writing into a file requires significant amount of
> work within the innermost test loop and also error handling.
>
> A simpler approach is to take advantage of volatile. Writing to a
> variable through a volatile pointer is enough to prevent compiler from
> optimizing the write away, and therefore compiler cannot remove the
> read loop either.
>
> Add a volatile 'value_sink' into resctrl_tests.c and make fill_buf to
> write into it. As a result, the error handling in fill_buf.c can be
> simplified.
>

The subject and changelog describes the need for a volatile variable.
The patch introduces two volatile variables. Could you please elaborate
why two volatile variables are needed?

Reinette