Adding Tony and Linux-OMAP cc:, as this patchset was written specifically with the OMAP in mind (thread rooted at http://lkml.org/lkml/2010/9/10/104 ). Any comments would be appreciated. Phil On 10/09/10 11:54 +0200, Carmody Phil.2 (EXT-Ixonos/Helsinki) wrote: > > The motivation for patch 2/3 is that currently our OMAP calibrates > itself using the trial-and-error binary chop fallback that some other > architectures no longer need to perform. This is a lengthy process, > taking 0.2s in an environment where boot time is of great interest. > > The patch has two optimisations. Firstly, it replaces the initial > repeated-doubling to find the relevant power of 2 with a tight loop > that just does as much as it can in a jiffy. Secondly, it doesn't > binary chop over an entire power of 2 range, it choses a much smaller > range based on how much it squeezed in, and failed to squeeze in, > during the first stage. Both are significant optimisations, and > bring our calibration down from 23 jiffies to 6, and, in the process, > arrive at a more accurate lpj value. > > The 'bands' and 'sub-logarithmic' growth may look over-engineered, > but they cost a small level of in inaccuracy of the initial guess > (for all architectures) in order to avoid the very large inaccuracies > that appeared during testing (on x86_64 architectures, and presumably > others with less metronomic operation). Note that due to the existence > of the TSC and other timers, the x86_64 doesn't use this fallback > routine, but I wanted to code defensively, able to cope with all kinds > of processor behaviours. > > 1/3 is simply cosmetic to prepare for 2/3. > 3/3 is simply to assist testing and not intended for integration. > > I would appreciate it if people with exotic or unusual architectures > could help test this. > > Cheers, > Phil > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
