On 09/07/2018 05:25 AM, Peter Zijlstra wrote:
On Thu, Aug 30, 2018 at 01:24:58PM -0700, subhra mazumdar wrote:+void pipe_busy_wait(struct pipe_inode_info *pipe) +{ + unsigned long wait_flag = pipe->pipe_wait_flag; + unsigned long start_time = pipe_busy_loop_current_time(); + + pipe_unlock(pipe); + preempt_disable(); + for (;;) { + if (pipe->pipe_wait_flag > wait_flag) { + preempt_enable(); + pipe_lock(pipe); + return; + } + if (pipe_busy_loop_timeout(pipe, start_time)) + break; + cpu_relax(); + } + preempt_enable(); + pipe_lock(pipe); + if (pipe->pipe_wait_flag > wait_flag) + return; + pipe_wait(pipe); +} + +void wake_up_busy_poll(struct pipe_inode_info *pipe) +{ + pipe->pipe_wait_flag++; +}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.
