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malloc: stop reading the subzone if MALLOC_DEBUG_MAXZONES == 1 (the default)

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malloc was showing at the top of profile during while running microbenchmarks.

#define DTMALLOC_PROBE_MAX              2
struct malloc_type_internal {
        uint32_t        mti_probes[DTMALLOC_PROBE_MAX];
        u_char          mti_zone;
        struct malloc_type_stats        mti_stats[MAXCPU];
};

Reading mti_zone it wastes a cacheline to hold mti_probes + mti_zone
(which we know is 0) + part of malloc stats of the first cpu which on top
induces false-sharing.

In particular will-it-scale lock1_processes -t 128 -s 10:
before: average:45879692
after:  average:51655596

Note the counters can be padded but the right fix is to move them to
counter(9), leaving the struct read-only after creation (modulo dtrace
probes).
This commit is contained in:
Mateusz Guzik 2018-04-23 22:28:49 +00:00
parent 4204224162
commit c9e05ccd62
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=332896
1 changed files with 36 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

55
sys/kern/kern_malloc.c
View File

@ -296,22 +296,49 @@ SYSCTL_UINT(_debug_malloc, OID_AUTO, zone_offset, CTLFLAG_RDTUN,
&zone_offset, 0, "Separate malloc types by examining the "
"Nth character in the malloc type short description.");
static u_int
mtp_get_subzone(const char *desc)
static void
mtp_set_subzone(struct malloc_type *mtp)
{
struct malloc_type_internal *mtip;
const char *desc;
size_t len;
u_int val;
mtip = mtp->ks_handle;
desc = mtp->ks_shortdesc;
if (desc == NULL || (len = strlen(desc)) == 0)
return (0);
val = desc[zone_offset % len];
return (val % numzones);
val = 0;
else
val = desc[zone_offset % len];
mtip->mti_zone = (val % numzones);
}
static inline u_int
mtp_get_subzone(struct malloc_type *mtp)
{
struct malloc_type_internal *mtip;
mtip = mtp->ks_handle;
KASSERT(mtip->mti_zone < numzones,
("mti_zone %u out of range %d",
mtip->mti_zone, numzones));
return (mtip->mti_zone);
}
#elif MALLOC_DEBUG_MAXZONES == 0
#error "MALLOC_DEBUG_MAXZONES must be positive."
#else
static void
mtp_set_subzone(struct malloc_type *mtp)
{
struct malloc_type_internal *mtip;
mtip = mtp->ks_handle;
mtip->mti_zone = 0;
}
static inline u_int
mtp_get_subzone(const char *desc)
mtp_get_subzone(struct malloc_type *mtp)
{
return (0);
@ -521,7 +548,6 @@ void *
malloc(size_t size, struct malloc_type *mtp, int flags)
{
int indx;
struct malloc_type_internal *mtip;
caddr_t va;
uma_zone_t zone;
#if defined(DEBUG_REDZONE)
@ -534,14 +560,10 @@ malloc(size_t size, struct malloc_type *mtp, int flags)
#endif
if (size <= kmem_zmax) {
mtip = mtp->ks_handle;
if (size & KMEM_ZMASK)
size = (size & ~KMEM_ZMASK) + KMEM_ZBASE;
indx = kmemsize[size >> KMEM_ZSHIFT];
KASSERT(mtip->mti_zone < numzones,
("mti_zone %u out of range %d",
mtip->mti_zone, numzones));
zone = kmemzones[indx].kz_zone[mtip->mti_zone];
zone = kmemzones[indx].kz_zone[mtp_get_subzone(mtp)];
#ifdef MALLOC_PROFILE
krequests[size >> KMEM_ZSHIFT]++;
#endif
@ -571,7 +593,6 @@ malloc_domain(size_t size, struct malloc_type *mtp, int domain,
int flags)
{
int indx;
struct malloc_type_internal *mtip;
caddr_t va;
uma_zone_t zone;
#if defined(DEBUG_REDZONE)
@ -583,14 +604,10 @@ malloc_domain(size_t size, struct malloc_type *mtp, int domain,
return (va);
#endif
if (size <= kmem_zmax) {
mtip = mtp->ks_handle;
if (size & KMEM_ZMASK)
size = (size & ~KMEM_ZMASK) + KMEM_ZBASE;
indx = kmemsize[size >> KMEM_ZSHIFT];
KASSERT(mtip->mti_zone < numzones,
("mti_zone %u out of range %d",
mtip->mti_zone, numzones));
zone = kmemzones[indx].kz_zone[mtip->mti_zone];
zone = kmemzones[indx].kz_zone[mtp_get_subzone(mtp)];
#ifdef MALLOC_PROFILE
krequests[size >> KMEM_ZSHIFT]++;
#endif
@ -973,7 +990,7 @@ malloc_init(void *data)
mtip = uma_zalloc(mt_zone, M_WAITOK | M_ZERO);
mtp->ks_handle = mtip;
mtip->mti_zone = mtp_get_subzone(mtp->ks_shortdesc);
mtp_set_subzone(mtp);
mtx_lock(&malloc_mtx);
mtp->ks_next = kmemstatistics;