On 02/12/2016 03:23 PM, Peter Zijlstra wrote:
On Fri, Feb 12, 2016 at 12:32:12PM -0500, Waiman Long wrote:
This patch adds a new waiter parameter to the mutex_optimistic_spin()
function to prepare it to be used by a waiter-spinner that doesn't
need to go into the OSQ as there can only be one waiter-spinner which
is the head of the waiting queue.
Does not explain why..
static bool mutex_optimistic_spin(struct mutex *lock,
+ struct ww_acquire_ctx *ww_ctx,
+ const bool use_ww_ctx, int waiter)
{
struct task_struct *task = current;
+ bool acquired = false;
+ if (!waiter) {
+ if (!mutex_can_spin_on_owner(lock))
+ goto done;
Why doesn't the waiter have to check mutex_can_spin_on_owner() ?
The reason why regular spinner need to call mutex_can_spin_on_owner is
because we want to avoid the overhead of the OSQ if we can't spin. As
mutex_can_spin_on_owner() is similar to mutex_spin_on_owner(), the
waiter-spinner will exit spinning after calling mutex_spin_on_owner().
Cheers,
Longman
