On 01/03/15 at 11:02am, Stephen Hemminger wrote:
> As a follow on to Thomas's patch I think this would complete the
> transistion to RCU for netlink.
> Compile tested only.
>
>
>
> This patch gets rid of the reader/writer nl_table_lock and replaces it
> with exclusively using RCU for reading, and a mutex for writing.
>
> Signed-off-by: Stephen Hemminger <step...@networkplumber.org>
I like it. One thing I noticed it that it leaves a mix of
native mutex unlocks and unlocks via netlink_table_ungrab().
The Open vSwitch upcall is a pretty good real world Netlink
benchmark. I'll run the tests I have to see if this has any
unexpected side effects.
> void netlink_table_grab(void)
> - __acquires(nl_table_lock)
> {
> - might_sleep();
> -
> - write_lock_irq(&nl_table_lock);
> -
> - if (atomic_read(&nl_table_users)) {
> - DECLARE_WAITQUEUE(wait, current);
> -
> - add_wait_queue_exclusive(&nl_table_wait, &wait);
> - for (;;) {
> - set_current_state(TASK_UNINTERRUPTIBLE);
> - if (atomic_read(&nl_table_users) == 0)
> - break;
> - write_unlock_irq(&nl_table_lock);
> - schedule();
> - write_lock_irq(&nl_table_lock);
> - }
> -
> - __set_current_state(TASK_RUNNING);
> - remove_wait_queue(&nl_table_wait, &wait);
> - }
> + mutex_lock(&nl_table_mutex);
> }
I left this untouched so far as I wasn't clear on what side effect
it would have to remove this as it does explicitely relax writers
right now.
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