Messages in this thread | | | Subject | Re: Does process need to have a kernel-side stack all the time? | From | "Denis V. Lunev" <> | Date | Mon, 14 Apr 2008 18:17:29 +0400 |
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On Mon, 2008-04-14 at 15:47 +0200, Denys Vlasenko wrote: > Hi Ingo, > > You are one of the experts in processes/threads and scheduling > in Linux kernel, I hope you can answer this question. > > A lot of effort went into minimizing of stack usage. > If I understand it correctly, one of the reasons for this > was to be efficient and not have lots of pages > used for stacks when we have a lot of threads > (tens of thousands). > > A random thought occurred to me: in a system with so many > threads most of them are not executing anyway, even on > that gigantic Altix machines. Do they all need to have > kernel stack, all the time? I mean: the process which > is running in user space is not using kernel stack at all. > Process which is not running on a CPU right now > is not using it either. But they do still consume > at least 4k (or 8k on 64bits) of RAM. > > Process absolutely must have kernel stack only when > it is actively running in kernel code (not sleeping), > right? > > Can we have per-CPU kernel stacks instead, so that process > gets a kernel stack only every time it enters the kernel; > and make it so that the process which is scheduled away > from a CPU does not need to have kernel stack? > > Currently, when process sleeps, we save some > state in stack, and such a change may require > some substantial surgery. > > Can you tell me whether this is possible at all, > and how difficult you estimate it to be?
I do not think that this can help. Usually, the process (thread) invokes some syscall like sleep and goes to the waiting state _from the kernel_, i.e. the kernel stack is used at that moment and will be required during wake up.
Regards, Den
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