On Tue, Aug 06, 2024 at 04:06:39AM +0000, Konstantin Belousov wrote:
> The branch main has been updated by kib:
>
> URL:
> https://cgit.FreeBSD.org/src/commit/?id=ff1ae3b3639d39a6485cfc655bf565cd04b9caa6
>
> commit ff1ae3b3639d39a6485cfc655bf565cd04b9caa6
> Author: Konstantin Belousov <[email protected]>
> AuthorDate: 2023-08-23 23:29:50 +0000
> Commit: Konstantin Belousov <[email protected]>
> CommitDate: 2024-08-06 04:05:58 +0000
>
> rangelocks: restore caching of the single rl entry in the struct thread
>
> Reviewed by: markj, Olivier Certner <[email protected]>
> Tested by: pho
> Sponsored by: The FreeBSD Foundation
> Differential revision: https://reviews.freebsd.org/D41787
> ---
> sys/kern/kern_rangelock.c | 33 +++++++++++++++++++++++++++------
> sys/kern/kern_thread.c | 1 +
> sys/sys/rangelock.h | 1 +
> 3 files changed, 29 insertions(+), 6 deletions(-)
>
> diff --git a/sys/kern/kern_rangelock.c b/sys/kern/kern_rangelock.c
> index 355b2125dd9b..2f16569b19aa 100644
> --- a/sys/kern/kern_rangelock.c
> +++ b/sys/kern/kern_rangelock.c
> @@ -82,8 +82,15 @@ static struct rl_q_entry *
> rlqentry_alloc(vm_ooffset_t start, vm_ooffset_t end, int flags)
> {
> struct rl_q_entry *e;
> -
> - e = uma_zalloc_smr(rl_entry_zone, M_WAITOK);
> + struct thread *td;
> +
> + td = curthread;
> + if (td->td_rlqe != NULL) {
> + e = td->td_rlqe;
> + td->td_rlqe = NULL;
> + } else {
> + e = uma_zalloc_smr(rl_entry_zone, M_WAITOK);
> + }
> e->rl_q_next = NULL;
> e->rl_q_free = NULL;
> e->rl_q_start = start;
> @@ -95,6 +102,12 @@ rlqentry_alloc(vm_ooffset_t start, vm_ooffset_t end, int
> flags)
> return (e);
> }
>
> +void
> +rangelock_entry_free(struct rl_q_entry *e)
> +{
> + uma_zfree_smr(rl_entry_zone, e);
> +}
> +
> void
> rangelock_init(struct rangelock *lock)
> {
> @@ -106,6 +119,7 @@ void
> rangelock_destroy(struct rangelock *lock)
> {
> struct rl_q_entry *e, *ep;
> + struct thread *td;
>
> MPASS(!lock->sleepers);
> for (e = (struct rl_q_entry *)atomic_load_ptr(&lock->head);
> @@ -386,8 +400,10 @@ rangelock_lock_int(struct rangelock *lock, bool trylock,
> vm_ooffset_t start,
> vm_ooffset_t end, int locktype)
> {
> struct rl_q_entry *e, *free, *x, *xp;
> + struct thread *td;
> enum RL_INSERT_RES res;
>
> + td = curthread;
> for (res = RL_LOCK_RETRY; res == RL_LOCK_RETRY;) {
> free = NULL;
> e = rlqentry_alloc(start, end, locktype);
> @@ -401,10 +417,15 @@ rangelock_lock_int(struct rangelock *lock, bool
> trylock, vm_ooffset_t start,
> e = NULL;
> }
> for (x = free; x != NULL; x = xp) {
> - MPASS(!rl_e_is_marked(x));
> - xp = x->rl_q_free;
> - MPASS(!rl_e_is_marked(xp));
> - uma_zfree_smr(rl_entry_zone, x);
> + MPASS(!rl_e_is_marked(x));
> + xp = x->rl_q_free;
> + MPASS(!rl_e_is_marked(xp));
> + if (td->td_rlqe == NULL) {
> + smr_synchronize(rl_smr);
I think I had the impression that this was a rare case, but empirically
it is not. As far as I can see, this smr_synchronize() call happens
every time an entry is freed, which could be very frequent.
smr_synchronize() bumps the global sequence counter and blocks until all
CPUs have had a chance to observe the new value, so is quite expensive.
I didn't try benchmarking yet, but pwrite3 from will-it-scale should be
a good candidate.
Why do we maintain this per-thread cache at all? IMO it would make more
sense to unconditionally free the entry here. Or perhaps I'm missing
something here.
> + td->td_rlqe = x;
> + } else {
> + uma_zfree_smr(rl_entry_zone, x);
> + }
> }
> }
> return (e);
> diff --git a/sys/kern/kern_thread.c b/sys/kern/kern_thread.c
> index c951e7297c89..9c3694feb945 100644
> --- a/sys/kern/kern_thread.c
> +++ b/sys/kern/kern_thread.c
> @@ -480,6 +480,7 @@ thread_fini(void *mem, int size)
> EVENTHANDLER_DIRECT_INVOKE(thread_fini, td);
> turnstile_free(td->td_turnstile);
> sleepq_free(td->td_sleepqueue);
> + rangelock_entry_free(td->td_rlqe);
> umtx_thread_fini(td);
> MPASS(td->td_sel == NULL);
> }
> diff --git a/sys/sys/rangelock.h b/sys/sys/rangelock.h
> index 310371bef879..60f394b67677 100644
> --- a/sys/sys/rangelock.h
> +++ b/sys/sys/rangelock.h
> @@ -65,6 +65,7 @@ void *rangelock_wlock(struct rangelock *lock,
> vm_ooffset_t start,
> vm_ooffset_t end);
> void *rangelock_trywlock(struct rangelock *lock, vm_ooffset_t start,
> vm_ooffset_t end);
> +void rangelock_entry_free(struct rl_q_entry *e);
> #if defined(INVARIANTS) || defined(INVARIANT_SUPPORT)
> void _rangelock_cookie_assert(void *cookie, int what, const char *file,
> int line);
