d/freebsd-dev
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

pipe: try to skip locking the pipe if a non-blocking fd is used

Browse Source 
Reviewed by:	markj (previous version)
Differential Revision:	https://reviews.freebsd.org/D36082
This commit is contained in:
Mateusz Guzik 2022-08-08 18:02:15 +00:00
parent 60dae3b83b
commit 9ac6eda6c6
1 changed files with 20 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

20
sys/kern/sys_pipe.c
View File

@ -721,6 +721,26 @@ pipe_read(struct file *fp, struct uio *uio, struct ucred *active_cred,
int size;
rpipe = fp->f_data;
/*
* Try to avoid locking the pipe if we have nothing to do.
*
* There are programs which share one pipe amongst multiple processes
* and perform non-blocking reads in parallel, even if the pipe is
* empty. This in particular is the case with BSD make, which when
* spawned with a high -j number can find itself with over half of the
* calls failing to find anything.
*/
if ((fp->f_flag & FNONBLOCK) != 0 && !mac_pipe_check_read_enabled()) {
if (__predict_false(uio->uio_resid == 0))
return (0);
if ((atomic_load_short(&rpipe->pipe_state) & PIPE_EOF) != 0)
return (0);
if (atomic_load_int(&rpipe->pipe_buffer.cnt) == 0 &&
atomic_load_int(&rpipe->pipe_pages.cnt) == 0)
return (EAGAIN);
}
PIPE_LOCK(rpipe);
++rpipe->pipe_busy;
error = pipelock(rpipe, 1);