Hi Elad, On 10/23/07, Elad Lahav <elad_lahav@xxxxxxxxxxxxxxxxxxxxx> wrote: > What do you mean by a context switch? > There are several terms that are sometimes confused with a context switch: > 1. Mode switch: The switch between user mode and kernel mode that occurs, > for example, at the beginning and end of a system call > 2. Address-space switch: Before a thread becomes active, it needs its > address space to be set as the current one (if it not already is). On the > x86, this happens by setting the cr3 register and flushing the TLB. > 3. The classic, OS course, context switch: This signifies the switch between > two processes, and may include multilple mode switches and an address-space > switch. Thank you for this elaborate clarification. I was indeed interested in #3, although #1 and #2 are also interesting. > I'm not sure there is an easy way to measure #3, as it probably varies > considerably depending on the scenario. The same goes for #2, as the cost > of TLB flushes cannot be determined a-priori, and depends on how many TLB > faults result from the switch. But is there a rough estimation of their cost ? tens of microseconds ? hundreds of microseconds ? several miliseconds ? I do not want accurate numbers. I just want to understand and to have a good hunch.. > As for #1, this is more manageable. I have taken some measurements in the > past by comparing a calculation that is performed entirely in user space, > vs. the same computation alternating between modes. Do you roughly remember the results ? Thank you so much naziir -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
