[PATCH 4/5] select: make select() use schedule_hrtimeout()

Arjan van de Ven
2008-08-29T15:21:55Z

From: Arjan van de Ven <arjan@linux.intel.com>
Date: Thu, 28 Aug 2008 13:45:38 -0700
Subject: [PATCH] select: make select() use schedule_hrtimeout()

now that we have schedule_hrtimeout(), make select() use it.
But only for short delays; really long delays are assumed to not
need the highres level of accuracy but rather want the regular
timer behavior for now.

This is only done for delays shorter than 1 second; currently
the assumption is that longer delays have no desire to get the
higher accuracy.

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
---
fs/select.c | 41 +++++++++++++++++++++++++++++------------
1 files changed, 29 insertions(+), 12 deletions(-)

diff --git a/fs/select.c b/fs/select.c
index 3ce5943..62b9767 100644
--- a/fs/select.c
+++ b/fs/select.c
@@ -24,6 +24,7 @@
#include <linux/fdtable.h>
#include <linux/fs.h>
#include <linux/rcupdate.h>
+#include <linux/hrtimer.h>

#include <asm/uaccess.h>

@@ -187,6 +188,7 @@ int do_select(int n, fd_set_bits *fds, s64 *timeout, struct timespec *end_time)
struct poll_wqueues table;
poll_table *wait;
int retval, i;
+ int use_hr = 0;

rcu_read_lock();
retval = max_select_fd(n, fds);
@@ -196,6 +198,10 @@ int do_select(int n, fd_set_bits *fds, s64 *timeout, struct timespec *end_time)
return retval;
n = retval;

+ /* Use hrtimers only for short timeouts for now */
+ if (*timeout < HZ && end_time->tv_sec != 0)
+ use_hr = 1;
+
poll_initwait(&table);
wait = &table.pt;
if (!*timeout)
@@ -266,20 +272,31 @@ int do_select(int n, fd_set_bits *fds, s64 *timeout, struct timespec *end_time)
break;
}

- if (*timeout < 0) {
- /* Wait indefinitely */
- __timeout = MAX_SCHEDULE_TIMEOUT;
- } else if (unlikely(*timeout >= (s64)MAX_SCHEDULE_TIMEOUT - 1)) {
- /* Wait for longer than MAX_SCHEDULE_TIMEOUT. Do it in a loop */
- __timeout = MAX_SCHEDULE_TIMEOUT - 1;
- *timeout -= __timeout;
+ if (use_hr) {
+ struct timespec now;
+ ktime_t expire;
+ schedule_hrtimeout(end_time, HRTIMER_MODE_ABS);
+ getnstimeofday(&now);
+ expire = ktime_sub(timespec_to_ktime(*end_time), timespec_to_ktime(now));
+ if (ktime_to_ns(expire) <= 0)
+ break;
+
} else {
- __timeout = *timeout;
- *timeout = 0;
+ if (*timeout < 0) {
+ /* Wait indefinitely */
+ __timeout = MAX_SCHEDULE_TIMEOUT;
+ } else if (unlikely(*timeout >= (s64)MAX_SCHEDULE_TIMEOUT - 1)) {
+ /* Wait for longer than MAX_SCHEDULE_TIMEOUT. Do it in a loop */
+ __timeout = MAX_SCHEDULE_TIMEOUT - 1;
+ *timeout -= __timeout;
+ } else {
+ __timeout = *timeout;
+ *timeout = 0;
+ }
+ __timeout = schedule_timeout(__timeout);
+ if (*timeout >= 0)
+ *timeout += __timeout;
}
- __timeout = schedule_timeout(__timeout);
- if (*timeout >= 0)
- *timeout += __timeout;
}
__set_current_state(TASK_RUNNING);

--
1.5.5.1