On Wed, Jan 07, 2015 at 10:14:07PM +0000, Catalin Marinas wrote: > On 7 January 2015 at 20:53, Russell King - ARM Linux > <li...@arm.linux.org.uk> wrote: > > Now, if I understand Linus correctly, what irks him is when someone > > upgrades a kernel on a platform, and some userland breaks. That's > > something which I've said multiple times I don't have a problem > > agreeing with, and I suspect no one in this thread would disagree > > that this is a serious failing, and one which needs fixing ASAP. > > Agree. But I assume you refer to the fact that we removed the BogoMIPS > reporting. It's fine to have it reverted. > > > However, if running userland on platform A works, and but it doesn't > > work on platform B. The breakage may well be due to platform A reporting > > 300 bogomips because it's using the kernel software loop, and platform > > B reporting 6 bogomips because its using a hardware timer, but the CPU > > is actually faster. However, this is not a kernel problem, and it > > certainly is not a regression. It's a userspace bug which needs > > userspace to fix. > > We need to look back at the point we added timer-based delay about 2.5 > years ago. Prior to commit d0a533b18235d362, platform A reported > bogomips 300. After that commit, the *same* platform A (not B), > started reported 6.
Correct. > Is the above considered user breakage? That's what Nico is trying to > solve. If we are fine with it, than we can close this thread, no > further changes needed. It's not a regression - yet. No one has shown that userspace has broken according to the definition of the first quote above, and that's the whole point. > We can document it as Linus suggests and say that prior to whatever > version we had 2.5 years ago, BogoMIPS was based on a busy loop. In > more recent kernels, it is based on a timer delay. User space should > make use of such information when interpreting BogoMIPS. We don't need to document it - we just need to point people at this URL: http://en.wikipedia.org/wiki/BogoMips which already describes it fully, including the existing ARM timer behaviour. -- FTTC broadband for 0.8mile line: currently at 9.5Mbps down 400kbps up according to speedtest.net. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
