forked from pool/systemd
47 lines
2.1 KiB
Diff
47 lines
2.1 KiB
Diff
From b63c8d4f0364457b0ead8793504012bb7113974f Mon Sep 17 00:00:00 2001
|
|
From: David Herrmann <dh.herrmann@gmail.com>
|
|
Date: Thu, 10 Jul 2014 00:47:23 +0200
|
|
Subject: [PATCH] sd-event: always call epoll_ctl() on mask-updates if
|
|
edge-triggered
|
|
|
|
A call to sd_event_source_set_io_events() skipps calling into the kernel
|
|
if the new event-mask matches the old one. This is safe for
|
|
level-triggered sources as the kernel moves them onto the ready-list
|
|
automatically if events change. However, edge-triggered sources might not
|
|
be on the ready-list even though events are present.
|
|
|
|
A call to sd_event_source_set_io_events() with EPOLLET set might thus be
|
|
used to just move the io-source onto the ready-list so the next poll
|
|
will return it again. This is very useful to avoid starvation in
|
|
priority-based event queues.
|
|
|
|
Imagine a read() loop on an edge-triggered fd. If we cannot read data fast
|
|
enough to drain the receive queue, we might decide to skip reading for now
|
|
and schedule it for later. On edge-triggered io-sources we have to make
|
|
sure it's put on the ready-list so the next dispatch-round will return it
|
|
again if it's still the highest priority task. We could make sd-event
|
|
handle edge-triggered sources directly and allow marking them ready again.
|
|
However, it's much simpler to let the kernel do that for now via
|
|
EPOLL_CTL_MOD.
|
|
---
|
|
src/libsystemd/sd-event/sd-event.c | 3 ++-
|
|
1 file changed, 2 insertions(+), 1 deletion(-)
|
|
|
|
diff --git src/libsystemd/sd-event/sd-event.c src/libsystemd/sd-event/sd-event.c
|
|
index 53f1904..a21f7db 100644
|
|
--- src/libsystemd/sd-event/sd-event.c
|
|
+++ src/libsystemd/sd-event/sd-event.c
|
|
@@ -1282,7 +1282,8 @@ _public_ int sd_event_source_set_io_events(sd_event_source *s, uint32_t events)
|
|
assert_return(s->event->state != SD_EVENT_FINISHED, -ESTALE);
|
|
assert_return(!event_pid_changed(s->event), -ECHILD);
|
|
|
|
- if (s->io.events == events)
|
|
+ /* edge-triggered updates are never skipped, so we can reset edges */
|
|
+ if (s->io.events == events && !(events & EPOLLET))
|
|
return 0;
|
|
|
|
if (s->enabled != SD_EVENT_OFF) {
|
|
--
|
|
1.7.9.2
|
|
|