On 09/17/2018 03:43 PM, Peter Zijlstra wrote:
On Mon, Sep 17, 2018 at 02:05:40PM -0700, Subhra Mazumdar wrote:
On 09/07/2018 05:25 AM, Peter Zijlstra wrote:
Why not just busy wait on current->state ? A little something like:
diff --git a/fs/pipe.c b/fs/pipe.c
index bdc5d3c0977d..8d9f1c95ff99 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -106,6 +106,7 @@ void pipe_double_lock(struct pipe_inode_info *pipe1,
void pipe_wait(struct pipe_inode_info *pipe)
{
DEFINE_WAIT(wait);
+ u64 start;
/*
* Pipes are system-local resources, so sleeping on them
@@ -113,7 +114,15 @@ void pipe_wait(struct pipe_inode_info *pipe)
*/
prepare_to_wait(&pipe->wait, &wait, TASK_INTERRUPTIBLE);
pipe_unlock(pipe);
- schedule();
+
+ preempt_disable();
+ start = local_clock();
+ while (!need_resched() && current->state != TASK_RUNNING &&
+ (local_clock() - start) < pipe->poll_usec)
+ cpu_relax();
+ schedule_preempt_disabled();
+ preempt_enable();
+
finish_wait(&pipe->wait, &wait);
pipe_lock(pipe);
}
This will make the current thread always spin and block as it itself does
the state change to TASK_RUNNING in finish_wait.
Nah, the actual wakeup will also do that state change. The one in
finish_wait() is for the case where the wait condition became true
without wakeup, such that we don't 'leak' the INTERRUPTIBLE state.
Ok, it works. I see similar improvements with hackbench as the original
patch.
