Messages in this thread |  | | | From | Andi Kleen <> | | Subject | Re: FOR REVIEW: New x86-64 vsyscall vgetcpu() | | Date | Fri, 16 Jun 2006 16:56:40 +0200 |
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On Friday 16 June 2006 14:36, Zoltan Menyhart wrote: > Just to make sure I understand it correctly... > Assuming I have allocated per CPU data (numa control, etc.) pointed at by: > > void *per_cpu[MAXCPUS];
That is not how user space TLS works. It usually has a base a register.
> > Assuming a per CPU variable has got an "offset" in each per CPU data area. > Accessing this variable can be done as follows: > > err = vgetcpu(&my_cpu, ...); > if (err) > goto .... > pointer = (typeof pointer) (per_cpu[my_cpu] + offset); > // use "pointer"... > > It is hundred times more long than "__get_per_cpu(var)++".
14 cycles is not a 100 times longer.
> My idea is to map the current task structure at an arch. dependent > virtual address into the user space (obviously in RO). > > #define current ((struct task_struct *) 0x...)
This means it cannot be cache colored (because you would need a static offset) and you couldn't share task_structs on a page.
Also you would make task_struct part of the userland ABI which seems like a very very bad idea to me. It means we couldn't change it anymore.
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