2014-04-07 13:57, Bruce Richardson: > This reverts commit da6fd0759cbeb5fc14991a79e40105b9f6b99059. > > The use of cpuinfo to determine the frequency of the TSC is not > advisable and leads to incorrect results when power management is > in use. This is because, while the TSC frequency does not change > in modern cpus with constant_tsc support, the frequency of the core, > and hence the frequency of the core reported by cpuinfo *does* change. > > Depending on the current frequency of core 0 when an application is > started, the EAL can get a wildly incorrect value for the TSC freq. > Since frequency is scaled down for power saving, any incorrect value > is likely to be lower than the default, which means that any delay > loops inside the code which rely on the TSC will be shorter than > planned. This can cause issues (reported on the mailing list by a number > of people) where ports are not initialized correctly due to delays being > too short. > > Signed-off-by: Bruce Richardson <bruce.richardson at intel.com>
I agree that using CPU frequency for TSC calibration is wrong with constant_tsc support. The goal was to have a precise calibration but the result is the reverse because of constant TSC. Acked and applied. Thank you Bruce for catching this. -- Thomas
