On Mon, 2004-07-12 at 16:58, Anand wrote: > Hi Folks, > I have few doubts on how memory is managed in Multi Processor > Systems(SMP)? Symmetrical Multi Processing. > Right now Linux uses 3G:1G split for a uniprocessor (Though patches are > there for 32G) > > 1) I was jus wondering how the 1G memory is managed on a SMP? > Suppose i have a 1Gig RAM and 3 procesors (32 bit),Is the 1 Gig memory split > among the 3 processors ?? > Since each processor can address 4G memory ,Do they have large Virtual > Address space? The memory is accessible by the 3 cpus, the word shared is more appropriate. > 2) How is the process switching taken care on SMP? > (ie) on a UP when when a process time slice is over ,its context is saved in > the PSW or the task_struct! > and next time it gets its timeslice , it loads the info form the > task_struct, > but on a SMP, Assume i have 3 procesors ,In the first time slice the Process > runs in Processor P1, > Is it possible for the process to run in Processor P2 when it gets it time > slice back ? > If possibe how is it taken care? Yes, a process doesn't have to stay on a particular cpu (unless you tell it to). On x86 the user space context is saved on the start of the kernel mode stack when entering the kernel mode (possibly through a timer tick). On the way back to user space it checks if need_resched is set, and if so will change to a new task. So there is no problem with having tasks run on different cpus. > 3)Does the Linux scheduler diffrenciates between a Process and a thread ? > All i can see in the scheduler code is a the task represented by > task_struct, which is getting scheduled, > >From which i assume ,that the scheduler schedules only the Process (coz > task_struct represents a Process :-)!!) > But how is the user space threads (which is part of a Process),Kernel treads > scheduled ? The scheduler sees things as tasks and nothing else, linux doesn't really make a distinction here. Kernel threads are normal tasks that execute in the kernel and they don't have their own mm_struct, they borrow someone elses. "User space threads" are treated as tasks. Hope this clears some up, I can recommend reading Robert Love's "Linux kernel development" -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
