On Sun, Sep 3, 2023 at 1:10 PM Kuan-Wei Chiu <visitorckw@xxxxxxxxx> wrote: > > On Sun, Sep 03, 2023 at 06:30:58PM +0500, Roman Mamedov wrote: > > On Sun, 3 Sep 2023 17:50:59 +0800 > > Kuan-Wei Chiu <visitorckw@xxxxxxxxx> wrote: > > > > > Replace the conditional statements in the cmp_stripe() function with a > > > branchless version to improve code readability and potentially enhance > > > performance. > > > > The new code will always do two comparisons and a subtraction (3 > > instructions in total), whereas the old version could return after just 1 > > comparison, or after 2 comparisons. So depending on the data values it is 3x > > to 1.5x as much operations performed than before, there unlikely to be any > > enhancement of performance. > > > > Also IMO the previous version is more easily readable. > > > The reason behind my proposed changes was to eliminate conditional > branches in the code. While the original code could occasionally achieve > early returns, many compilers, such as x86-64 gcc 13.2 compiling with > -O2 flag, still generate branch instructions. Processors typically have > deep pipelines, and a branch prediction miss can result in a high > penalty. Therefore, even though early return might not be possible, the > new branchless version of code could still offer efficiency > improvements. We need more information to support the efficiency improvement here. In this case, I would like to see some benchmark results (micro benchmark is fine). If we cannot show the difference in performance, I would rather keep current code. Thanks, Song [...]
