On Tue, Jun 01, 2021 at 08:23:24AM +1000, David Gwynne wrote:
>
> > On 1 Jun 2021, at 02:58, Visa Hankala <v...@hankala.org> wrote:
> >
> > This patch enables the pool cache feature on the knote pool to reduce
> > the overhead of knote management.
> >
> > Profiling done by mpi@ and bluhm@ indicate that the potentially needless
> > allocation of knotes in kqueue_register() causes slowdown with
> > kqueue-based poll(2) and select(2).
> >
> > One approach to fix this is to reverse the function's initial guess
> > about knote: Try without allocation first. Then allocate and retry if
> > the knote is missing from the kqueue and EV_ADD is given.
> >
> > Another option is to cache free knotes so that the shared knote pool
> > would be accessed less frequently.
> >
> > The following diff takes the second approach. The caching is implemented
> > simply by enabling the pool cache feature. This makes use of existing
> > code and does not complicate kqueue_register(). The feature also helps
> > if there is heavy knote churn.
> >
> > I think the most substantial part of the diff is that it extends pool
> > cache usage beyond mbufs. Is this change acceptable?
>
> absolutely.
>
> > Note the cache is not particularly useful without kqueue-based poll(2)
> > and select(2). The pool view of systat(1) shows that there are pools
> > that would benefit more than knote_pool from caching, at least in terms
> > of request frequencies. The relative frequencies are dependent on system
> > workload, though. Kqpoll would definitely make knote pool more heavily
> > used.
>
> ok.
>
> separate to this diff, at some point maybe we should have a task list/dohook
> thing for "per cpu init" like mountroot or startup?
At first I fumbled with a deferring version of pool_cache_init() but the
idea felt overly specific. However, a more general dohook might indeed
make sense.
It is a bit unfortunate that the deferring is needed at all, though.
The number of different boot-time deferral options gets larger as well.
The diff below omits a manual page.
Index: kern/init_main.c
===================================================================
RCS file: src/sys/kern/init_main.c,v
retrieving revision 1.306
diff -u -p -r1.306 init_main.c
--- kern/init_main.c 8 Feb 2021 10:51:01 -0000 1.306
+++ kern/init_main.c 1 Jun 2021 15:29:05 -0000
@@ -432,6 +432,9 @@ main(void *framep)
prof_init();
#endif
+ /* Run hooks that require the presence of all CPUs. */
+ dopercpuhooks();
+
mbcpuinit(); /* enable per cpu mbuf data */
uvm_init_percpu();
Index: kern/kern_subr.c
===================================================================
RCS file: src/sys/kern/kern_subr.c,v
retrieving revision 1.50
diff -u -p -r1.50 kern_subr.c
--- kern/kern_subr.c 29 Apr 2018 17:26:31 -0000 1.50
+++ kern/kern_subr.c 1 Jun 2021 15:29:05 -0000
@@ -198,6 +198,8 @@ hashfree(void *hash, int elements, int t
* "startup hook" types, functions, and variables.
*/
+struct hook_desc_head percpuhook_list =
+ TAILQ_HEAD_INITIALIZER(percpuhook_list);
struct hook_desc_head startuphook_list =
TAILQ_HEAD_INITIALIZER(startuphook_list);
Index: sys/systm.h
===================================================================
RCS file: src/sys/sys/systm.h,v
retrieving revision 1.153
diff -u -p -r1.153 systm.h
--- sys/systm.h 28 Apr 2021 09:42:04 -0000 1.153
+++ sys/systm.h 1 Jun 2021 15:29:05 -0000
@@ -283,6 +283,9 @@ void wdog_register(int (*)(void *, int),
void wdog_shutdown(void *);
/*
+ * Per-CPU hooks are functions that are run after all CPUs have been detected
+ * but before the scheduler has started.
+ *
* Startup hooks are functions running after the scheduler has started
* but before any threads have been created or root has been mounted.
*/
@@ -294,6 +297,7 @@ struct hook_desc {
};
TAILQ_HEAD(hook_desc_head, hook_desc);
+extern struct hook_desc_head percpuhook_list;
extern struct hook_desc_head startuphook_list;
void *hook_establish(struct hook_desc_head *, int, void (*)(void *), void *);
@@ -303,6 +307,12 @@ void dohooks(struct hook_desc_head *, in
#define HOOK_REMOVE 0x01
#define HOOK_FREE 0x02
+#define percpuhook_establish(fn, arg) \
+ hook_establish(&percpuhook_list, 1, (fn), (arg))
+#define percpuhook_disestablish(vhook) \
+ hook_disestablish(&percpuhook_list, (vhook))
+#define dopercpuhooks() dohooks(&percpuhook_list, HOOK_REMOVE|HOOK_FREE)
+
#define startuphook_establish(fn, arg) \
hook_establish(&startuphook_list, 1, (fn), (arg))
#define startuphook_disestablish(vhook) \
