Re: idle task's task_t allocation on NUMA machines

[Eric Dumazet <dada1@cosmosbay.com>]

Samuel Thibault a écrit :
> Hi,
> 
> Currently, the task_t structure of the idle task is always allocated
> on CPU0, hence on node 0: while booting, for each CPU, CPU 0 calls
> fork_idle(), hence copy_process(), hence dup_task_struct(), hence
> alloc_task_struct(), hence kmem_cache_alloc(), which picks up memory
> from the allocation cache of the current CPU, i.e. on node 0.
> 
> This is a bad idea: every write needs be written back to node 0 at some
> time, so that node 0 can get a small bit busy especially when other
> nodes are idle.
> 
> A solution would be to add to copy_process(), dup_task_struct(),
> alloc_task_struct() and kmem_cache_alloc() the node number on which
> allocation should be performed. This might also be useful if performing
> node load balancing at fork(): one could then allocate task_t directly
> on the new node. It might also be useful when allocating data for
> another node.
> 
> Regards,
> Samuel

An idle task should block itself, hence not touching its task_t structure very much.

I believe IRQ stacks are also allocated on node 0, that seems more serious.

Eric