On Tue, Nov 22, 2005 at 12:02:12PM +0200, Rafi Gordon wrote: > Is the cost , in terms of CPU , when there occurs a context switch > between two kernel threads is the same as when > there is a context switch between two user space threads ?
userspace threads are mapped to kernel threads in Linux (more accurately, userspace threads are represented by tasks in a 1-1 mapping). > Is this cost the same when there is a context switch between a kernel > thread and a user space thread ? No. A switch between userspace threads in Linux requires switching to kernel space first. There's no support by default for userspace threading. > If you look at the implementation of kernel_thread() method (in i386 it's in > arch/i386/kernel/process.c), you will see that it ultimately > calls do_fork() ; in fact also when you create a user space process/thread by > fork() or pthread_create() you also ultimately call do_fork(). > > There are of course some differences between kernel threads > and user space threads. > for example : a kernel thread does not have any need for access to memory > of user space. > > But do these differences cause a conetxt switch between 2 kernel > threads to be quicker ? Yes. Since there's no need to switch address spaces or priviledge levels to ctx switch between two kernel threads, it's just th overhead of the scheduler and ctx_switch itself. Cheers, Muli -- Muli Ben-Yehuda http://www.mulix.org | http://mulix.livejournal.com/ ================================================================= To unsubscribe, send mail to [EMAIL PROTECTED] with the word "unsubscribe" in the message body, e.g., run the command echo unsubscribe | mail [EMAIL PROTECTED]
