Author: mmacy
Date: Thu May 17 00:45:35 2018
New Revision: 333695
URL: https://svnweb.freebsd.org/changeset/base/333695
Log:
epoch(9): Guarantee forward progress on busy sections
Add epoch section to struct thread. We can use this to
ennable epoch counter to advance even if a section is
perpetually occupied by a thread.
Approved by: sbruno
Modified:
head/sys/kern/subr_epoch.c
head/sys/sys/proc.h
Modified: head/sys/kern/subr_epoch.c
==============================================================================
--- head/sys/kern/subr_epoch.c Wed May 16 23:42:02 2018 (r333694)
+++ head/sys/kern/subr_epoch.c Thu May 17 00:45:35 2018 (r333695)
@@ -54,7 +54,7 @@ __FBSDID("$FreeBSD$");
static MALLOC_DEFINE(M_EPOCH, "epoch", "epoch based reclamation");
/* arbitrary --- needs benchmarking */
-#define MAX_ADAPTIVE_SPIN 5000
+#define MAX_ADAPTIVE_SPIN 1000
#define EPOCH_EXITING 0x1
#ifdef __amd64__
@@ -63,6 +63,7 @@ static MALLOC_DEFINE(M_EPOCH, "epoch", "epoch based re
#define EPOCH_ALIGN CACHE_LINE_SIZE
#endif
+CTASSERT(sizeof(epoch_section_t) == sizeof(ck_epoch_section_t));
SYSCTL_NODE(_kern, OID_AUTO, epoch, CTLFLAG_RW, 0, "epoch information");
SYSCTL_NODE(_kern_epoch, OID_AUTO, stats, CTLFLAG_RW, 0, "epoch stats");
@@ -308,8 +309,12 @@ epoch_enter(epoch_t epoch)
KASSERT(found, ("recursing on a second epoch"));
}
#endif
+ if (td->td_epochnest > 1) {
+ critical_exit();
+ return;
+ }
sched_pin();
- ck_epoch_begin(&eps->eps_record.er_record, NULL);
+ ck_epoch_begin(&eps->eps_record.er_record,
(ck_epoch_section_t*)&td->td_epoch_section);
critical_exit();
}
@@ -324,11 +329,15 @@ epoch_exit(epoch_t epoch)
MPASS(td->td_epochnest);
critical_enter();
eps = epoch->e_pcpu[curcpu];
- sched_unpin();
- ck_epoch_end(&eps->eps_record.er_record, NULL);
td->td_epochnest--;
if (td->td_epochnest == 0)
TAILQ_REMOVE(&eps->eps_record.er_tdlist, td, td_epochq);
+ else {
+ critical_exit();
+ return;
+ }
+ sched_unpin();
+ ck_epoch_end(&eps->eps_record.er_record,
(ck_epoch_section_t*)&td->td_epoch_section);
eps->eps_record.er_gen++;
critical_exit();
}
Modified: head/sys/sys/proc.h
==============================================================================
--- head/sys/sys/proc.h Wed May 16 23:42:02 2018 (r333694)
+++ head/sys/sys/proc.h Thu May 17 00:45:35 2018 (r333695)
@@ -76,6 +76,18 @@
/*
+ * A section object may be passed to every begin-end pair to allow for
+ * forward progress guarantees with-in prolonged active sections.
+ *
+ * We can't include ck_epoch.h so we define our own variant here and
+ * then CTASSERT that it's the same size in subr_epoch.c
+ */
+struct epoch_section {
+ unsigned int bucket;
+};
+typedef struct epoch_section epoch_section_t;
+
+/*
* One structure allocated per session.
*
* List of locks
@@ -352,6 +364,7 @@ struct thread {
struct proc *td_rfppwait_p; /* (k) The vforked child */
struct vm_page **td_ma; /* (k) uio pages held */
int td_ma_cnt; /* (k) size of *td_ma */
+ epoch_section_t td_epoch_section; /* (t) epoch section object */
void *td_emuldata; /* Emulator state data */
int td_lastcpu; /* (t) Last cpu we were on. */
int td_oncpu; /* (t) Which cpu we are on. */
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