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Add some global counters for SMR. These may eventually become per-smr

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counters.  In my stress test there is only one poll for every 15,000
frees.  This means we are effectively amortizing the cache coherency
overhead even with very high write rates (3M/s/core).

Reviewed by:	markj, rlibby
Differential Revision:	https://reviews.freebsd.org/D23463
This commit is contained in:
Jeff Roberson 2020-02-06 20:10:21 +00:00
parent 7295d1dda1
commit 8d7f16a5db
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=357637
1 changed files with 32 additions and 3 deletions
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35
sys/kern/subr_smr.c
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@ -30,11 +30,13 @@ __FBSDID("$FreeBSD$");
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/limits.h>
#include <sys/counter.h>
#include <sys/kernel.h>
#include <sys/limits.h>
#include <sys/proc.h>
#include <sys/smp.h>
#include <sys/smr.h>
#include <sys/sysctl.h>
#include <vm/uma.h>
@ -162,6 +164,17 @@ static uma_zone_t smr_zone;
#define SMR_SEQ_MAX_ADVANCE SMR_SEQ_MAX_DELTA / 2
#endif
static SYSCTL_NODE(_debug, OID_AUTO, smr, CTLFLAG_RW, NULL, "SMR Stats");
static counter_u64_t advance = EARLY_COUNTER;
SYSCTL_COUNTER_U64(_debug_smr, OID_AUTO, advance, CTLFLAG_RD, &advance, "");
static counter_u64_t advance_wait = EARLY_COUNTER;
SYSCTL_COUNTER_U64(_debug_smr, OID_AUTO, advance_wait, CTLFLAG_RD, &advance_wait, "");
static counter_u64_t poll = EARLY_COUNTER;
SYSCTL_COUNTER_U64(_debug_smr, OID_AUTO, poll, CTLFLAG_RD, &poll, "");
static counter_u64_t poll_scan = EARLY_COUNTER;
SYSCTL_COUNTER_U64(_debug_smr, OID_AUTO, poll_scan, CTLFLAG_RD, &poll_scan, "");
/*
* Advance the write sequence and return the new value for use as the
* wait goal. This guarantees that any changes made by the calling
@ -197,14 +210,17 @@ smr_advance(smr_t smr)
*/
s = zpcpu_get(smr)->c_shared;
goal = atomic_fetchadd_int(&s->s_wr_seq, SMR_SEQ_INCR) + SMR_SEQ_INCR;
counter_u64_add(advance, 1);
/*
* Force a synchronization here if the goal is getting too
* far ahead of the read sequence number. This keeps the
* wrap detecting arithmetic working in pathological cases.
*/
if (goal - atomic_load_int(&s->s_rd_seq) >= SMR_SEQ_MAX_DELTA)
if (goal - atomic_load_int(&s->s_rd_seq) >= SMR_SEQ_MAX_DELTA) {
counter_u64_add(advance_wait, 1);
smr_wait(smr, goal - SMR_SEQ_MAX_ADVANCE);
}
return (goal);
}
@ -263,6 +279,7 @@ smr_poll(smr_t smr, smr_seq_t goal, bool wait)
success = true;
critical_enter();
s = zpcpu_get(smr)->c_shared;
counter_u64_add_protected(poll, 1);
/*
* Acquire barrier loads s_wr_seq after s_rd_seq so that we can not
@ -306,6 +323,7 @@ smr_poll(smr_t smr, smr_seq_t goal, bool wait)
* gone inactive. Keep track of the oldest sequence currently
* active as rd_seq.
*/
counter_u64_add_protected(poll_scan, 1);
rd_seq = s_wr_seq;
CPU_FOREACH(i) {
c = zpcpu_get_cpu(smr, i);
@ -366,7 +384,7 @@ smr_poll(smr_t smr, smr_seq_t goal, bool wait)
s_rd_seq = atomic_load_int(&s->s_rd_seq);
do {
if (SMR_SEQ_LEQ(rd_seq, s_rd_seq))
break;
goto out;
} while (atomic_fcmpset_int(&s->s_rd_seq, &s_rd_seq, rd_seq) == 0);
out:
@ -426,3 +444,14 @@ smr_init(void)
smr_zone = uma_zcreate("SMR CPU", sizeof(struct smr),
NULL, NULL, NULL, NULL, (CACHE_LINE_SIZE * 2) - 1, UMA_ZONE_PCPU);
}
static void
smr_init_counters(void *unused)
{
advance = counter_u64_alloc(M_WAITOK);
advance_wait = counter_u64_alloc(M_WAITOK);
poll = counter_u64_alloc(M_WAITOK);
poll_scan = counter_u64_alloc(M_WAITOK);
}
SYSINIT(smr_counters, SI_SUB_CPU, SI_ORDER_ANY, smr_init_counters, NULL);