On 15/07/2021 20:49, Mark Michelson wrote:
Hi Anton,
Out of curiosity, has this change made a noticeable impact on
performance?
I can't pick it up on OVN heater.
That is not unexpected. It is "noise" compared to the compute time and
the number of syscalls used in one iteration in northd or ovsdb.
I suspect it will be more useful in places like the vswitch itself where
the loops are tighter, processing per loop is less and lower latency is
the key. There, one syscall less per iteration may show up as a
noticeable difference.
I do not have a benchmark set up for those.
A.
On 7/12/21 1:15 PM, [email protected] wrote:
From: Anton Ivanov <[email protected]>
time_poll() makes an excessive number of time_msec() calls
which incur a performance penalty.
1. Avoid time_msec() call for timeout calculation when time_poll()
is asked to skip poll()
2. Reuse the time_msec() result from deadline calculation for
last_wakeup and timeout calculation.
Signed-off-by: Anton Ivanov <[email protected]>
---
lib/timeval.c | 36 +++++++++++++++++++++---------------
1 file changed, 21 insertions(+), 15 deletions(-)
diff --git a/lib/timeval.c b/lib/timeval.c
index c6ac87376..64ab22e05 100644
--- a/lib/timeval.c
+++ b/lib/timeval.c
@@ -287,7 +287,7 @@ time_poll(struct pollfd *pollfds, int n_pollfds,
HANDLE *handles OVS_UNUSED,
long long int timeout_when, int *elapsed)
{
long long int *last_wakeup = last_wakeup_get();
- long long int start;
+ long long int start, now;
bool quiescent;
int retval = 0;
@@ -297,28 +297,31 @@ time_poll(struct pollfd *pollfds, int
n_pollfds, HANDLE *handles OVS_UNUSED,
if (*last_wakeup && !thread_is_pmd()) {
log_poll_interval(*last_wakeup);
}
- start = time_msec();
+ now = start = time_msec();
timeout_when = MIN(timeout_when, deadline);
quiescent = ovsrcu_is_quiescent();
for (;;) {
- long long int now = time_msec();
int time_left;
- if (now >= timeout_when) {
+ if (n_pollfds == 0) {
time_left = 0;
- } else if ((unsigned long long int) timeout_when - now >
INT_MAX) {
- time_left = INT_MAX;
} else {
- time_left = timeout_when - now;
- }
-
- if (!quiescent) {
- if (!time_left) {
- ovsrcu_quiesce();
+ if (now >= timeout_when) {
+ time_left = 0;
+ } else if ((unsigned long long int) timeout_when - now >
INT_MAX) {
+ time_left = INT_MAX;
} else {
- ovsrcu_quiesce_start();
+ time_left = timeout_when - now;
+ }
+
+ if (!quiescent) {
+ if (!time_left) {
+ ovsrcu_quiesce();
+ } else {
+ ovsrcu_quiesce_start();
+ }
}
}
@@ -329,6 +332,8 @@ time_poll(struct pollfd *pollfds, int
n_pollfds, HANDLE *handles OVS_UNUSED,
*/
if (n_pollfds != 0) {
retval = poll(pollfds, n_pollfds, time_left);
+ } else {
+ retval = 0;
}
if (retval < 0) {
retval = -errno;
@@ -355,7 +360,8 @@ time_poll(struct pollfd *pollfds, int n_pollfds,
HANDLE *handles OVS_UNUSED,
ovsrcu_quiesce_end();
}
- if (deadline <= time_msec()) {
+ now = time_msec();
+ if (deadline <= now) {
#ifndef _WIN32
fatal_signal_handler(SIGALRM);
#else
@@ -372,7 +378,7 @@ time_poll(struct pollfd *pollfds, int n_pollfds,
HANDLE *handles OVS_UNUSED,
break;
}
}
- *last_wakeup = time_msec();
+ *last_wakeup = now;
refresh_rusage();
*elapsed = *last_wakeup - start;
return retval;
--
Anton R. Ivanov
Cambridgegreys Limited. Registered in England. Company Number 10273661
https://www.cambridgegreys.com/
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