> Date: Fri, 11 Dec 2020 11:51:54 -0600
> From: Scott Cheloha <[email protected]>
>
> 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.
Yes. The consequence of that is that the values are no longer
patchable. That may not be very important though (I never really use
that possibility).
> > 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 */
>
>
