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amd64 pmap: block on turnstile for lock-less DI.
Port the code to block on turnstile instead of yielding, to lock-less delayed invalidation. The yield might cause tight loop due to priority inversion. Since it is impossible to avoid race between block and wake-up, arm 1-tick callout to wakeup when thread blocks itself. Reported and tested by: mjg Reviewed by: alc, markj Sponsored by: The FreeBSD Foundation MFC after: 2 months Differential revision: https://reviews.freebsd.org/D20636
This commit is contained in:
Konstantin Belousov
parent
7a3a48426e
commit
d8ddb98a5e
Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=349326
@ -484,6 +484,9 @@ static struct pmap_invl_gen pmap_invl_gen_head = {
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.next = NULL,
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};
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static u_long pmap_invl_gen = 1;
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static int pmap_invl_waiters;
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static struct callout pmap_invl_callout;
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static bool pmap_invl_callout_inited;
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#define PMAP_ASSERT_NOT_IN_DI() \
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KASSERT(pmap_not_in_di(), ("DI already started"))
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@ -538,6 +541,34 @@ pmap_thread_init_invl_gen_l(struct thread *td)
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invl_gen->gen = 0;
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}
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static void
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pmap_delayed_invl_wait_block(u_long *m_gen, u_long *invl_gen)
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{
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struct turnstile *ts;
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ts = turnstile_trywait(&invl_gen_ts);
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if (*m_gen > atomic_load_long(invl_gen))
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turnstile_wait(ts, NULL, TS_SHARED_QUEUE);
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else
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turnstile_cancel(ts);
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}
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static void
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pmap_delayed_invl_finish_unblock(u_long new_gen)
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{
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struct turnstile *ts;
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turnstile_chain_lock(&invl_gen_ts);
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ts = turnstile_lookup(&invl_gen_ts);
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if (new_gen != 0)
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pmap_invl_gen = new_gen;
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if (ts != NULL) {
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turnstile_broadcast(ts, TS_SHARED_QUEUE);
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turnstile_unpend(ts);
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}
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turnstile_chain_unlock(&invl_gen_ts);
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}
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/*
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* Start a new Delayed Invalidation (DI) block of code, executed by
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* the current thread. Within a DI block, the current thread may
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@ -582,24 +613,15 @@ static void
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pmap_delayed_invl_finish_l(void)
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{
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struct pmap_invl_gen *invl_gen, *next;
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struct turnstile *ts;
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invl_gen = &curthread->td_md.md_invl_gen;
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KASSERT(invl_gen->gen != 0, ("missed invl_start"));
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mtx_lock(&invl_gen_mtx);
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next = LIST_NEXT(invl_gen, link);
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if (next == NULL) {
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turnstile_chain_lock(&invl_gen_ts);
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ts = turnstile_lookup(&invl_gen_ts);
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pmap_invl_gen = invl_gen->gen;
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if (ts != NULL) {
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turnstile_broadcast(ts, TS_SHARED_QUEUE);
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turnstile_unpend(ts);
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}
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turnstile_chain_unlock(&invl_gen_ts);
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} else {
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if (next == NULL)
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pmap_delayed_invl_finish_unblock(invl_gen->gen);
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else
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next->gen = invl_gen->gen;
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}
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LIST_REMOVE(invl_gen, link);
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mtx_unlock(&invl_gen_mtx);
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invl_gen->gen = 0;
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@ -856,6 +878,8 @@ pmap_delayed_invl_finish_u(void)
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goto again;
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}
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critical_exit();
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if (atomic_load_int(&pmap_invl_waiters) > 0)
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pmap_delayed_invl_finish_unblock(0);
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if (invl_gen->saved_pri != 0) {
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thread_lock(td);
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sched_prio(td, invl_gen->saved_pri);
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@ -888,6 +912,9 @@ DB_SHOW_COMMAND(di_queue, pmap_di_queue)
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static long invl_wait;
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SYSCTL_LONG(_vm_pmap, OID_AUTO, invl_wait, CTLFLAG_RD, &invl_wait, 0,
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"Number of times DI invalidation blocked pmap_remove_all/write");
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static long invl_wait_slow;
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SYSCTL_LONG(_vm_pmap, OID_AUTO, invl_wait_slow, CTLFLAG_RD, &invl_wait_slow, 0,
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"Number of slow invalidation waits for lockless DI");
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#endif
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static u_long *
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@ -897,6 +924,27 @@ pmap_delayed_invl_genp(vm_page_t m)
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return (&pv_invl_gen[pa_index(VM_PAGE_TO_PHYS(m)) % NPV_LIST_LOCKS]);
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}
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static void
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pmap_delayed_invl_callout_func(void *arg __unused)
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{
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if (atomic_load_int(&pmap_invl_waiters) == 0)
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return;
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pmap_delayed_invl_finish_unblock(0);
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}
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static void
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pmap_delayed_invl_callout_init(void *arg __unused)
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{
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if (pmap_di_locked())
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return;
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callout_init(&pmap_invl_callout, 1);
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pmap_invl_callout_inited = true;
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}
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SYSINIT(pmap_di_callout, SI_SUB_CPU + 1, SI_ORDER_ANY,
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pmap_delayed_invl_callout_init, NULL);
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/*
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* Ensure that all currently executing DI blocks, that need to flush
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* TLB for the given page m, actually flushed the TLB at the time the
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@ -914,7 +962,6 @@ pmap_delayed_invl_genp(vm_page_t m)
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static void
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pmap_delayed_invl_wait_l(vm_page_t m)
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{
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struct turnstile *ts;
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u_long *m_gen;
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#ifdef PV_STATS
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bool accounted = false;
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@ -928,11 +975,7 @@ pmap_delayed_invl_wait_l(vm_page_t m)
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accounted = true;
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}
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#endif
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ts = turnstile_trywait(&invl_gen_ts);
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if (*m_gen > pmap_invl_gen)
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turnstile_wait(ts, NULL, TS_SHARED_QUEUE);
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else
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turnstile_cancel(ts);
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pmap_delayed_invl_wait_block(m_gen, &pmap_invl_gen);
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}
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}
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@ -940,19 +983,53 @@ static void
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pmap_delayed_invl_wait_u(vm_page_t m)
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{
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u_long *m_gen;
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#ifdef PV_STATS
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bool accounted = false;
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#endif
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struct lock_delay_arg lda;
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bool fast;
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fast = true;
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m_gen = pmap_delayed_invl_genp(m);
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lock_delay_arg_init(&lda, &di_delay);
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while (*m_gen > atomic_load_long(&pmap_invl_gen_head.gen)) {
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#ifdef PV_STATS
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if (!accounted) {
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atomic_add_long(&invl_wait, 1);
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accounted = true;
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if (fast || !pmap_invl_callout_inited) {
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PV_STAT(atomic_add_long(&invl_wait, 1));
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lock_delay(&lda);
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fast = false;
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} else {
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/*
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* The page's invalidation generation number
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* is still below the current thread's number.
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* Prepare to block so that we do not waste
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* CPU cycles or worse, suffer livelock.
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*
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* Since it is impossible to block without
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* racing with pmap_delayed_invl_finish_u(),
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* prepare for the race by incrementing
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* pmap_invl_waiters and arming a 1-tick
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* callout which will unblock us if we lose
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* the race.
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*/
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atomic_add_int(&pmap_invl_waiters, 1);
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/*
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* Re-check the current thread's invalidation
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* generation after incrementing
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* pmap_invl_waiters, so that there is no race
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* with pmap_delayed_invl_finish_u() setting
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* the page generation and checking
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* pmap_invl_waiters. The only race allowed
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* is for a missed unblock, which is handled
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* by the callout.
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*/
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if (*m_gen >
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atomic_load_long(&pmap_invl_gen_head.gen)) {
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callout_reset(&pmap_invl_callout, 1,
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pmap_delayed_invl_callout_func, NULL);
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PV_STAT(atomic_add_long(&invl_wait_slow, 1));
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pmap_delayed_invl_wait_block(m_gen,
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&pmap_invl_gen_head.gen);
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}
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atomic_add_int(&pmap_invl_waiters, -1);
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}
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#endif
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kern_yield(PRI_USER);
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}
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}
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