On 11/01/2009 10:13 PM, loody wrote:
Dear all: I find the kernel use cpu instruction to implement the udelay function as keeping decrease a big counter by 1. If I search the right place in kernel, why kernel does so?
Because udelay is used in places where the kernel cannot use other mechanisms, eg. because interrupts are blocked or the current process cannot be scheduled out.
the precision will be different if cpu runs faster or slower, right?
At bootup the kernel measures the delay loop speed of each CPU. CPU frequency scaling might make the loop run slower at times, but that is okay because udelay simply specifies a *minimum* delay. This is true even on systems without frequency scaling, because the udelay loop could be interrupted by an interrupt, an NMI or by having the CPU trap into SMM mode and execute code there. -- All rights reversed. -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
