On Tue, 28 Nov 2023, Reinette Chatre wrote: > 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? Well, the other "volatile variable" is a pointer to a volatile variable. I've seen gcc to kill a static volatile int so I prefer to not take change with its optimizer. Thus, I placed the sink into different compilation unit and just present a pointer to the actual "volatile" variable. I guess the sink could be marked as plain int instead but this being trickery to begin with I don't see much value either way. It's still a trick. I'll alter the changelog's wording though, "a volatile variable" is not accurate as it's "a pointer to a volatile variable". -- i.
