On Tue, Aug 18, 2020 at 11:04:47AM +0200, Martin Pieuchot wrote:
> Diff below changes the order of operations in kqueue_register() to get
> rid of an unnecessary pool_get(). When an event is already present on
> the list try to acquire it first. Note that knote_acquire() may sleep
> in which case the list might have changed so the lookup has to always
> begin from the start.
>
> This will help with lazy removal of knote in poll/select. In this
> scenario EV_ADD is generally always done with an knote already on the
> list.
Some of the overhead could be absorbed by using a pool cache, as shown
in the diff below. However, I am not suggesting that the cache should
be taken into use right now. The frequency of knote pool usage is
relatively low currently; there are other pools that would benefit more
from caching.
A related question is what implications the increased use of the pool
cache feature would have under memory pressure.
Index: kern/init_main.c
===================================================================
RCS file: src/sys/kern/init_main.c,v
retrieving revision 1.300
diff -u -p -r1.300 init_main.c
--- kern/init_main.c 16 Jun 2020 05:09:29 -0000 1.300
+++ kern/init_main.c 18 Aug 2020 15:09:38 -0000
@@ -71,6 +71,7 @@
#include <sys/msg.h>
#endif
#include <sys/domain.h>
+#include <sys/event.h>
#include <sys/msgbuf.h>
#include <sys/mbuf.h>
#include <sys/pipe.h>
@@ -148,7 +149,6 @@ void crypto_init(void);
void db_ctf_init(void);
void prof_init(void);
void init_exec(void);
-void kqueue_init(void);
void futex_init(void);
void taskq_init(void);
void timeout_proc_init(void);
@@ -431,7 +431,9 @@ main(void *framep)
prof_init();
#endif
- mbcpuinit(); /* enable per cpu mbuf data */
+ /* Enable per cpu data. */
+ mbcpuinit();
+ kqueue_init_percpu();
/* init exec and emul */
init_exec();
Index: kern/kern_event.c
===================================================================
RCS file: src/sys/kern/kern_event.c,v
retrieving revision 1.142
diff -u -p -r1.142 kern_event.c
--- kern/kern_event.c 12 Aug 2020 13:49:24 -0000 1.142
+++ kern/kern_event.c 18 Aug 2020 15:09:38 -0000
@@ -205,6 +205,12 @@ kqueue_init(void)
PR_WAITOK, "knotepl", NULL);
}
+void
+kqueue_init_percpu(void)
+{
+ pool_cache_init(&knote_pool);
+}
+
int
filt_fileattach(struct knote *kn)
{
Index: sys/event.h
===================================================================
RCS file: src/sys/sys/event.h,v
retrieving revision 1.44
diff -u -p -r1.44 event.h
--- sys/event.h 22 Jun 2020 13:14:32 -0000 1.44
+++ sys/event.h 18 Aug 2020 15:09:38 -0000
@@ -210,6 +210,8 @@ extern void knote_activate(struct knote
extern void knote_remove(struct proc *p, struct knlist *list);
extern void knote_fdclose(struct proc *p, int fd);
extern void knote_processexit(struct proc *);
+extern void kqueue_init(void);
+extern void kqueue_init_percpu(void);
extern int kqueue_register(struct kqueue *kq,
struct kevent *kev, struct proc *p);
extern int filt_seltrue(struct knote *kn, long hint);
