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. 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. 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. Elad Ramagudi Naziir wrote: > Hi all - > > I am looking for a rule of thumb regarding the time it takes > to context switch in linux (any other OS comparison would be interesting > too) on a modern hardware (x86 is probably the most interesting, but > other numbers might be handy too if anyone has them). > > Thank you for any help on the matter ! > naziir > > -- > To unsubscribe from this list: send an email with > "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx > Please read the FAQ at http://kernelnewbies.org/FAQ -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
