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amd64 pmap: block on turnstile for lock-less DI.

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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 2019-06-23 21:21:11 +00:00
parent 7a3a48426e
commit d8ddb98a5e
1 changed files with 104 additions and 27 deletions
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131
sys/amd64/amd64/pmap.c
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@ -484,6 +484,9 @@ static struct pmap_invl_gen pmap_invl_gen_head = {
.next = NULL,
};
static u_long pmap_invl_gen = 1;
static int pmap_invl_waiters;
static struct callout pmap_invl_callout;
static bool pmap_invl_callout_inited;
#define PMAP_ASSERT_NOT_IN_DI() \
KASSERT(pmap_not_in_di(), ("DI already started"))
@ -538,6 +541,34 @@ pmap_thread_init_invl_gen_l(struct thread *td)
invl_gen->gen = 0;
}
static void
pmap_delayed_invl_wait_block(u_long *m_gen, u_long *invl_gen)
{
struct turnstile *ts;
ts = turnstile_trywait(&invl_gen_ts);
if (*m_gen > atomic_load_long(invl_gen))
turnstile_wait(ts, NULL, TS_SHARED_QUEUE);
else
turnstile_cancel(ts);
}
static void
pmap_delayed_invl_finish_unblock(u_long new_gen)
{
struct turnstile *ts;
turnstile_chain_lock(&invl_gen_ts);
ts = turnstile_lookup(&invl_gen_ts);
if (new_gen != 0)
pmap_invl_gen = new_gen;
if (ts != NULL) {
turnstile_broadcast(ts, TS_SHARED_QUEUE);
turnstile_unpend(ts);
}
turnstile_chain_unlock(&invl_gen_ts);
}
/*
* Start a new Delayed Invalidation (DI) block of code, executed by
* the current thread. Within a DI block, the current thread may
@ -582,24 +613,15 @@ static void
pmap_delayed_invl_finish_l(void)
{
struct pmap_invl_gen *invl_gen, *next;
struct turnstile *ts;
invl_gen = &curthread->td_md.md_invl_gen;
KASSERT(invl_gen->gen != 0, ("missed invl_start"));
mtx_lock(&invl_gen_mtx);
next = LIST_NEXT(invl_gen, link);
if (next == NULL) {
turnstile_chain_lock(&invl_gen_ts);
ts = turnstile_lookup(&invl_gen_ts);
pmap_invl_gen = invl_gen->gen;
if (ts != NULL) {
turnstile_broadcast(ts, TS_SHARED_QUEUE);
turnstile_unpend(ts);
}
turnstile_chain_unlock(&invl_gen_ts);
} else {
if (next == NULL)
pmap_delayed_invl_finish_unblock(invl_gen->gen);
else
next->gen = invl_gen->gen;
}
LIST_REMOVE(invl_gen, link);
mtx_unlock(&invl_gen_mtx);
invl_gen->gen = 0;
@ -856,6 +878,8 @@ pmap_delayed_invl_finish_u(void)
goto again;
}
critical_exit();
if (atomic_load_int(&pmap_invl_waiters) > 0)
pmap_delayed_invl_finish_unblock(0);
if (invl_gen->saved_pri != 0) {
thread_lock(td);
sched_prio(td, invl_gen->saved_pri);
@ -888,6 +912,9 @@ DB_SHOW_COMMAND(di_queue, pmap_di_queue)
static long invl_wait;
SYSCTL_LONG(_vm_pmap, OID_AUTO, invl_wait, CTLFLAG_RD, &invl_wait, 0,
"Number of times DI invalidation blocked pmap_remove_all/write");
static long invl_wait_slow;
SYSCTL_LONG(_vm_pmap, OID_AUTO, invl_wait_slow, CTLFLAG_RD, &invl_wait_slow, 0,
"Number of slow invalidation waits for lockless DI");
#endif
static u_long *
@ -897,6 +924,27 @@ pmap_delayed_invl_genp(vm_page_t m)
return (&pv_invl_gen[pa_index(VM_PAGE_TO_PHYS(m)) % NPV_LIST_LOCKS]);
}
static void
pmap_delayed_invl_callout_func(void *arg __unused)
{
if (atomic_load_int(&pmap_invl_waiters) == 0)
return;
pmap_delayed_invl_finish_unblock(0);
}
static void
pmap_delayed_invl_callout_init(void *arg __unused)
{
if (pmap_di_locked())
return;
callout_init(&pmap_invl_callout, 1);
pmap_invl_callout_inited = true;
}
SYSINIT(pmap_di_callout, SI_SUB_CPU + 1, SI_ORDER_ANY,
pmap_delayed_invl_callout_init, NULL);
/*
* Ensure that all currently executing DI blocks, that need to flush
* TLB for the given page m, actually flushed the TLB at the time the
@ -914,7 +962,6 @@ pmap_delayed_invl_genp(vm_page_t m)
static void
pmap_delayed_invl_wait_l(vm_page_t m)
{
struct turnstile *ts;
u_long *m_gen;
#ifdef PV_STATS
bool accounted = false;
@ -928,11 +975,7 @@ pmap_delayed_invl_wait_l(vm_page_t m)
accounted = true;
}
#endif
ts = turnstile_trywait(&invl_gen_ts);
if (*m_gen > pmap_invl_gen)
turnstile_wait(ts, NULL, TS_SHARED_QUEUE);
else
turnstile_cancel(ts);
pmap_delayed_invl_wait_block(m_gen, &pmap_invl_gen);
}
}
@ -940,19 +983,53 @@ static void
pmap_delayed_invl_wait_u(vm_page_t m)
{
u_long *m_gen;
#ifdef PV_STATS
bool accounted = false;
#endif
struct lock_delay_arg lda;
bool fast;
fast = true;
m_gen = pmap_delayed_invl_genp(m);
lock_delay_arg_init(&lda, &di_delay);
while (*m_gen > atomic_load_long(&pmap_invl_gen_head.gen)) {
#ifdef PV_STATS
if (!accounted) {
atomic_add_long(&invl_wait, 1);
accounted = true;
if (fast || !pmap_invl_callout_inited) {
PV_STAT(atomic_add_long(&invl_wait, 1));
lock_delay(&lda);
fast = false;
} else {
/*
* The page's invalidation generation number
* is still below the current thread's number.
* Prepare to block so that we do not waste
* CPU cycles or worse, suffer livelock.
*
* Since it is impossible to block without
* racing with pmap_delayed_invl_finish_u(),
* prepare for the race by incrementing
* pmap_invl_waiters and arming a 1-tick
* callout which will unblock us if we lose
* the race.
*/
atomic_add_int(&pmap_invl_waiters, 1);
/*
* Re-check the current thread's invalidation
* generation after incrementing
* pmap_invl_waiters, so that there is no race
* with pmap_delayed_invl_finish_u() setting
* the page generation and checking
* pmap_invl_waiters. The only race allowed
* is for a missed unblock, which is handled
* by the callout.
*/
if (*m_gen >
atomic_load_long(&pmap_invl_gen_head.gen)) {
callout_reset(&pmap_invl_callout, 1,
pmap_delayed_invl_callout_func, NULL);
PV_STAT(atomic_add_long(&invl_wait_slow, 1));
pmap_delayed_invl_wait_block(m_gen,
&pmap_invl_gen_head.gen);
}
atomic_add_int(&pmap_invl_waiters, -1);
}
#endif
kern_yield(PRI_USER);
}
}