On Fri, Dec 11, 2020 at 09:49:07AM -0300, Martin Pieuchot wrote:
> On 11/12/20(Fri) 12:52, Mark Kettenis wrote:
> > > Date: Thu, 10 Dec 2020 16:13:22 -0600
> > > From: Scott Cheloha <[email protected]>
> > >
> > > Hi,
> > >
> > > We looked at removing the ticks from subr_pool.c a while back but it
> > > got shelved. That may or may not have been my fault. I don't
> > > remember.
> > >
> > > Anyway, I would normally suggest switching to getuptime(9) here, but
> > > getuptime(9) counts in seconds and we're working with a 1 second
> > > timeout in this code (pool_wait_free) so that's too coarse an
> > > interface for this job.
> > >
> > > The next best thing I could come up with was introducing a coarse
> > > sub-second interface for use in this file, "getnsecuptime()", which
> > > calls getnanouptime(9) and converts the result to a 64-bit count of
> > > nanoseconds. This is relatively fast (we don't read the underlying
> > > timecounter hardware) and causes a minimal amount of code change (we
> > > can use it inline because it returns an integral value).
> > >
> > > >From there the changes are simple:
> > >
> > > - Renames: ph_tick -> ph_timestamp, pr_cache_tick -> pr_cache_timestamp
> > >
> > > - Call getnsecuptime(9) wherever we read 'ticks'.
> > >
> > > - Change pool_wait_gc and pool_wait_free to counts of nanoseconds.
> > > They could be macros, e.g.
> > >
> > > #define POOL_WAIT_GC 8000000000ULL
> > >
> > > but I'll leave that for a second diff to keep things simple.
> > >
> > > This compiles and I haven't changed any logic so I assume it isn't
> > > broken.
> > >
> > > We could move getnsecuptime() into kern_tc.c but it isn't used
> > > anywhere else yet so I'm hesitant to do so.
> > >
> > > Thoughts?
> >
> > Specifying the timeouts in nanoseconds isn't particularly useful I'd
> > say. But I see we can't use SEC_TO_NSEC here because of the overflow
> > check...
>
> I'm not sure to understand, can't we do:
>
> pool_wait_free = SEC_TO_NSEC(1);
> pool_wait_gc = SEC_TO_NSEC(8);
>
> or are you pointing at something else?
We can do that at runtime but not at compile time. SEC_TO_NSEC(1)
isn't a constant so that won't compile (I just tried).
We _could_ do something like this:
#define POOL_WAIT_FREE SEC_TO_NSEC(1)
I think the compiler will probably inline the result and elide the
overflow check because the input is a constant. I don't know how to
verify this, but my limited understanding of compilers suggests that
this is totally possible.
> One comment below
>
> [...]
>
> > > Index: sys/pool.h
> > > ===================================================================
> > > RCS file: /cvs/src/sys/sys/pool.h,v
> > > retrieving revision 1.77
> > > diff -u -p -r1.77 pool.h
> > > --- sys/pool.h 19 Jul 2019 09:03:03 -0000 1.77
> > > +++ sys/pool.h 10 Dec 2020 22:08:33 -0000
> > > @@ -201,7 +201,7 @@ struct pool {
> > > u_int pr_cache_items; /* target list length */
> > > u_int pr_cache_contention;
> > > u_int pr_cache_contention_prev;
> > > - int pr_cache_tick; /* time idle list was empty */
> > > + uint64_t pr_cache_timestamp; /* when idle list was empty */
> > > int pr_cache_nout;
>
> Do you see a change in of size in the struct? If so, does moving
> `pr_cache_nout' after `pr_cache_ngc' helps?
Right, the structs. We're changing both struct pool_page_header and
struct pool.
For the unmodified (-current) binary on amd64:
$ gdb -q obj/bsd.gdb
(gdb) p sizeof(struct pool_page_header)
$1 = 112
(gdb) p sizeof(struct pool)
$2 = 424
For the patched binary on amd64:
(gdb) p sizeof(struct pool_page_header)
$1 = 112
(gdb) p sizeof(struct pool)
$2 = 432
kettenis@: The pool_page_header does not grow. That's good, right?
If do as mpi@ suggested and we move pr_cache_nout after
pr_cache_ngc...
$ gdb -q obj/bsd.gdb
(gdb) p sizeof(struct pool_page_header)
$1 = 112
(gdb) p sizeof(struct pool)
$2 = 424
Bingo! Same size. mpi@, how did you know?
Patch attached with the struct shuffling and the new macros below.
Index: kern/subr_pool.c
===================================================================
RCS file: /cvs/src/sys/kern/subr_pool.c,v
retrieving revision 1.230
diff -u -p -r1.230 subr_pool.c
--- kern/subr_pool.c 24 Jan 2020 06:31:17 -0000 1.230
+++ kern/subr_pool.c 11 Dec 2020 17:50:46 -0000
@@ -41,6 +41,7 @@
#include <sys/syslog.h>
#include <sys/sysctl.h>
#include <sys/task.h>
+#include <sys/time.h>
#include <sys/timeout.h>
#include <sys/percpu.h>
@@ -148,7 +149,7 @@ struct pool_page_header {
caddr_t ph_page; /* this page's address */
caddr_t ph_colored; /* page's colored address */
unsigned long ph_magic;
- int ph_tick;
+ uint64_t ph_timestamp;
};
#define POOL_MAGICBIT (1 << 3) /* keep away from perturbed low bits */
#define POOL_PHPOISON(ph) ISSET((ph)->ph_magic, POOL_MAGICBIT)
@@ -266,8 +267,19 @@ void pool_gc_sched(void *);
struct timeout pool_gc_tick = TIMEOUT_INITIALIZER(pool_gc_sched, NULL);
void pool_gc_pages(void *);
struct task pool_gc_task = TASK_INITIALIZER(pool_gc_pages, NULL);
-int pool_wait_free = 1;
-int pool_wait_gc = 8;
+
+#define POOL_WAIT_FREE SEC_TO_NSEC(1)
+#define POOL_WAIT_GC SEC_TO_NSEC(8)
+
+/* XXX where do I put this? */
+uint64_t
+getnsecuptime(void)
+{
+ struct timespec now;
+
+ getnanouptime(&now);
+ return TIMESPEC_TO_NSEC(&now);
+}
RBT_PROTOTYPE(phtree, pool_page_header, ph_node, phtree_compare);
@@ -797,7 +809,7 @@ pool_put(struct pool *pp, void *v)
/* is it time to free a page? */
if (pp->pr_nidle > pp->pr_maxpages &&
(ph = TAILQ_FIRST(&pp->pr_emptypages)) != NULL &&
- (ticks - ph->ph_tick) > (hz * pool_wait_free)) {
+ getnsecuptime() - ph->ph_timestamp > POOL_WAIT_FREE) {
freeph = ph;
pool_p_remove(pp, freeph);
}
@@ -864,7 +876,7 @@ pool_do_put(struct pool *pp, void *v)
*/
pp->pr_nidle++;
- ph->ph_tick = ticks;
+ ph->ph_timestamp = getnsecuptime();
TAILQ_REMOVE(&pp->pr_partpages, ph, ph_entry);
TAILQ_INSERT_TAIL(&pp->pr_emptypages, ph, ph_entry);
pool_update_curpage(pp);
@@ -1566,7 +1578,7 @@ pool_gc_pages(void *null)
/* is it time to free a page? */
if (pp->pr_nidle > pp->pr_minpages &&
(ph = TAILQ_FIRST(&pp->pr_emptypages)) != NULL &&
- (ticks - ph->ph_tick) > (hz * pool_wait_gc)) {
+ getnsecuptime() - ph->ph_timestamp > POOL_WAIT_GC) {
freeph = ph;
pool_p_remove(pp, freeph);
} else
@@ -1726,7 +1738,7 @@ pool_cache_init(struct pool *pp)
arc4random_buf(pp->pr_cache_magic, sizeof(pp->pr_cache_magic));
TAILQ_INIT(&pp->pr_cache_lists);
pp->pr_cache_nitems = 0;
- pp->pr_cache_tick = ticks;
+ pp->pr_cache_timestamp = getnsecuptime();
pp->pr_cache_items = 8;
pp->pr_cache_contention = 0;
pp->pr_cache_ngc = 0;
@@ -1829,7 +1841,7 @@ pool_cache_list_free(struct pool *pp, st
{
pool_list_enter(pp);
if (TAILQ_EMPTY(&pp->pr_cache_lists))
- pp->pr_cache_tick = ticks;
+ pp->pr_cache_timestamp = getnsecuptime();
pp->pr_cache_nitems += POOL_CACHE_ITEM_NITEMS(ci);
TAILQ_INSERT_TAIL(&pp->pr_cache_lists, ci, ci_nextl);
@@ -2006,7 +2018,7 @@ pool_cache_gc(struct pool *pp)
{
unsigned int contention, delta;
- if ((ticks - pp->pr_cache_tick) > (hz * pool_wait_gc) &&
+ if (getnsecuptime() - pp->pr_cache_timestamp > POOL_WAIT_GC &&
!TAILQ_EMPTY(&pp->pr_cache_lists) &&
pl_enter_try(pp, &pp->pr_cache_lock)) {
struct pool_cache_item *pl = NULL;
@@ -2015,7 +2027,7 @@ pool_cache_gc(struct pool *pp)
if (pl != NULL) {
TAILQ_REMOVE(&pp->pr_cache_lists, pl, ci_nextl);
pp->pr_cache_nitems -= POOL_CACHE_ITEM_NITEMS(pl);
- pp->pr_cache_tick = ticks;
+ pp->pr_cache_timestamp = getnsecuptime();
pp->pr_cache_ngc++;
}
Index: sys/pool.h
===================================================================
RCS file: /cvs/src/sys/sys/pool.h,v
retrieving revision 1.77
diff -u -p -r1.77 pool.h
--- sys/pool.h 19 Jul 2019 09:03:03 -0000 1.77
+++ sys/pool.h 11 Dec 2020 17:50:46 -0000
@@ -201,9 +201,9 @@ struct pool {
u_int pr_cache_items; /* target list length */
u_int pr_cache_contention;
u_int pr_cache_contention_prev;
- int pr_cache_tick; /* time idle list was empty */
- int pr_cache_nout;
+ uint64_t pr_cache_timestamp; /* time idle list was empty */
uint64_t pr_cache_ngc; /* # of times the gc released a list */
+ int pr_cache_nout;
u_int pr_align;
u_int pr_maxcolors; /* Cache coloring */
