On Thu, Aug 01, 2002 at 03:50:34PM -0000, Pichai Raghavan wrote: > I have a requirement to lock the Linux scheduler; what I mean by > this is that when I enter the kernel mode in context of a > particular process, no other task (other than the idle task) > should be running. On an UP, scheduling becomes cooperative. So you can make sure you are not calling it in any way (beware that many things like kmalloc can schedule, but usualy there is a non-blocking variant or flag). On SMP (or with preempt patch) the situation is far worse, because on the other CPUs, the processes are currently running. > These are the various ways we have come up with: > (i) Moving all tasks in the running queue to interruptile queue > other than current and idle task. This way schedule() can never > get to run any other task. You sure don't want to make them interruptible. But even just puting them to uninterruptible state would however add some races (and processes that are already sleeping may be woken up anytime by an interrupt. So you probably end up signalling all other processes with SIGSTOP and waiting for them to actually get it. This is also only way to get around that a process might be running on onother CPU on SMP. > (ii) Changing schedule so that it does a while(1) as long as the > current task is not in the run queue. Once the current task is > runnable return immediately. You wouldn't need signals here. But you have to force schedule on all CPUs on SMP. In both cases, you must note, that things like kmalloc may wait on kernel threads (like kswapd, bdflush, perhaps even kreiserfsd and maybe others). If you don't let them to processor, you have to do everything non-blocking anyway. > Will the above ways work? Or there are better ways? One suggestion > I got was to use the goodness flag but I am not exactly sure. IIRC goodness flag is related to how scheduler chooses processes to run and it's too much scheduler internal that can change anytime (there are at least two completely different schedulers around these days). Perhaps if you said why do you need that, someone could come with more elegant solution for the whole problem. ------------------------------------------------------------------------------- Jan 'Bulb' Hudec <bulb@ucw.cz> -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
