On Thu, 29 Jan 2026 10:00:15 +0100 Morten Brørup <[email protected]> wrote:
> > This and previous proposal to prefetch have no impact on performance. > > Rolled a simple perf test and all three versions come out the same. > > Please be aware that many test cases are inadvertently designed in a way > where mbufs unintendedly are hot in the cache, so prefetching does not > provide the expected performance gain. > E.g. when working on a newly allocated mbuf, the mbuf should be cold. > But if it came from the mempool cache, and was recently worked on and then > freed into the mempool cache, then it will be hot. > > > The bottleneck is not here, probably at system call and copies now. > > The most important bottleneck might be elsewhere. > But this optimization might not be as irrelevant as the test results indicate. > > Anyway, I agree that dropping the patch (for now) makes sense. I doubt pre-fetch will matter much in a driver like this because: - on tx the data is still in cache since just setup by caller - on rx the data is still in cache since kernel just copied it into the buffer.
