Author: mjg
Date: Thu Nov 12 00:29:23 2020
New Revision: 367605
URL: https://svnweb.freebsd.org/changeset/base/367605
Log:
thread: move nthread management out of tid_alloc
While this adds more work single-threaded, it also enables SMP-related
speed ups.
Modified:
head/sys/kern/kern_thread.c
Modified: head/sys/kern/kern_thread.c
==============================================================================
--- head/sys/kern/kern_thread.c Wed Nov 11 22:35:23 2020 (r367604)
+++ head/sys/kern/kern_thread.c Thu Nov 12 00:29:23 2020 (r367605)
@@ -144,7 +144,7 @@ static int maxthread;
SYSCTL_INT(_kern, OID_AUTO, maxthread, CTLFLAG_RDTUN,
&maxthread, 0, "Maximum number of threads");
-static int nthreads;
+static __exclusive_cache_line int nthreads;
static LIST_HEAD(tidhashhead, thread) *tidhashtbl;
static u_long tidhash;
@@ -158,29 +158,52 @@ EVENTHANDLER_LIST_DEFINE(thread_dtor);
EVENTHANDLER_LIST_DEFINE(thread_init);
EVENTHANDLER_LIST_DEFINE(thread_fini);
-static lwpid_t
-tid_alloc(void)
+static bool
+thread_count_inc(void)
{
static struct timeval lastfail;
static int curfail;
- static lwpid_t trytid;
- lwpid_t tid;
+ int nthreads_new;
- mtx_lock(&tid_lock);
- if (nthreads + 1 >= maxthread - 100) {
+ thread_reap();
+
+ nthreads_new = atomic_fetchadd_int(&nthreads, 1) + 1;
+ if (nthreads_new >= maxthread - 100) {
if (priv_check_cred(curthread->td_ucred, PRIV_MAXPROC) != 0 ||
- nthreads + 1 >= maxthread) {
- mtx_unlock(&tid_lock);
+ nthreads_new >= maxthread) {
+ atomic_subtract_int(&nthreads, 1);
if (ppsratecheck(&lastfail, &curfail, 1)) {
printf("maxthread limit exceeded by uid %u "
"(pid %d); consider increasing
kern.maxthread\n",
curthread->td_ucred->cr_ruid, curproc->p_pid);
}
- return (-1);
+ return (false);
}
}
+ return (true);
+}
- nthreads++;
+static void
+thread_count_sub(int n)
+{
+
+ atomic_subtract_int(&nthreads, n);
+}
+
+static void
+thread_count_dec(void)
+{
+
+ thread_count_sub(1);
+}
+
+static lwpid_t
+tid_alloc(void)
+{
+ static lwpid_t trytid;
+ lwpid_t tid;
+
+ mtx_lock(&tid_lock);
/*
* It is an invariant that the bitmap is big enough to hold maxthread
* IDs. If we got to this point there has to be at least one free.
@@ -212,7 +235,6 @@ tid_free_locked(lwpid_t rtid)
KASSERT(bit_test(tid_bitmap, tid) != 0,
("thread ID %d not allocated\n", rtid));
bit_clear(tid_bitmap, tid);
- nthreads--;
}
static void
@@ -398,6 +420,10 @@ threadinit(void)
mtx_init(&tid_lock, "TID lock", NULL, MTX_DEF);
tid_bitmap = bit_alloc(maxthread, M_TIDHASH, M_WAITOK);
+ /*
+ * Handle thread0.
+ */
+ thread_count_inc();
tid0 = tid_alloc();
if (tid0 != THREAD0_TID)
panic("tid0 %d != %d\n", tid0, THREAD0_TID);
@@ -482,6 +508,7 @@ thread_reap(void)
thread_free_batched(itd);
if (tidbatchn == nitems(tidbatch)) {
tid_free_batch(tidbatch, tidbatchn);
+ thread_count_sub(tidbatchn);
tidbatchn = 0;
}
itd = ntd;
@@ -489,6 +516,7 @@ thread_reap(void)
if (tidbatchn != 0) {
tid_free_batch(tidbatch, tidbatchn);
+ thread_count_sub(tidbatchn);
}
}
@@ -501,18 +529,17 @@ thread_alloc(int pages)
struct thread *td;
lwpid_t tid;
- thread_reap(); /* check if any zombies to get */
-
- tid = tid_alloc();
- if (tid == -1) {
+ if (!thread_count_inc()) {
return (NULL);
}
+ tid = tid_alloc();
td = uma_zalloc(thread_zone, M_WAITOK);
KASSERT(td->td_kstack == 0, ("thread_alloc got thread with kstack"));
if (!vm_thread_new(td, pages)) {
uma_zfree(thread_zone, td);
tid_free(tid);
+ thread_count_dec();
return (NULL);
}
td->td_tid = tid;
@@ -564,6 +591,7 @@ thread_free(struct thread *td)
tid = td->td_tid;
thread_free_batched(td);
tid_free(tid);
+ thread_count_dec();
}
void
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