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Remove LLE read lock from IPv4 fast path.

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LLE structure is mostly unchanged during its lifecycle.
To be more specific, there are 2 things relevant for fast path
  lookup code:
1) link-level address change. Since r286722, these updates are performed
  under AFDATA WLOCK.
2) Some sort of feedback indicating that this particular entry is used so
  we re-send arp request to perform reachability verification instead of
  expiring entry. The only signal that is needed from fast path is something
  like binary yes/no.

The latter is solved by the following changes:
1) introduce special r_skip_req field which is read lockless by fast path,
  but updated under (new) req_mutex mutex. If this field is non-zero, then
  fast path will acquire lock and set it back to 0.
2) introduce simple state machine: incomplete->reachable<->verify->deleted.
  Before that we implicitely had incomplete->reachable->deleted state machine,
  with V_arpt_keep between "reachable" and "deleted". Verification was performed
  in runtime 5 seconds before V_arpt_keep expire.
  This is changed to "change state to verify 5 seconds before V_arpt_keep,
  set r_skip_req to non-zero value and check it every second". If the value
  is zero - then send arp verification probe.
These changes do not introduce any signifficant control plane overhead:
  typically lle callout timer would fire 1 time more each V_arpt_keep (1200s)
  for used lles and up to arp_maxtries (5) for dead lles.

As a result, all packets towards "reachable" lle are handled by fast path without
acquiring lle read lock.

Additional "req_mutex" is needed because callout / arpresolve_slow() or eventhandler
  might keep LLE lock for signifficant amount of time, which might not be feasible
  for fast path locking (e.g. having rmlock as ether AFDATA or lltable own lock).

Differential Revision:	https://reviews.freebsd.org/D3688
This commit is contained in:
Alexander V. Chernikov 2015-12-05 09:50:37 +00:00
parent c218815337
commit f8aee88f0b
4 changed files with 118 additions and 51 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
sys/net/if_llatbl.c
View File

@ -284,6 +284,7 @@ lltable_set_entry_addr(struct ifnet *ifp, struct llentry *lle,
bcopy(lladdr, &lle->ll_addr, ifp->if_addrlen);
lle->la_flags |= LLE_VALID;
lle->r_flags |= RLLE_VALID;
}
/*
@ -640,6 +641,7 @@ lla_rt_output(struct rt_msghdr *rtm, struct rt_addrinfo *info)
if ((rtm->rtm_flags & RTF_ANNOUNCE))
lle->la_flags |= LLE_PUB;
lle->la_flags |= LLE_VALID;
lle->r_flags |= RLLE_VALID;
lle->la_expire = rtm->rtm_rmx.rmx_expire;
laflags = lle->la_flags;

15
sys/net/if_llatbl.h
View File

@ -63,7 +63,8 @@ struct llentry {
uint16_t mac16[3];
uint8_t mac8[20]; /* IB needs 20 bytes. */
} ll_addr;
uint32_t spare0;
uint16_t r_flags; /* LLE runtime flags */
uint16_t r_skip_req; /* feedback from fast path */
uint64_t spare1;
struct lltable *lle_tbl;
@ -83,6 +84,7 @@ struct llentry {
LIST_ENTRY(llentry) lle_chain; /* chain of deleted items */
struct callout lle_timer;
struct rwlock lle_lock;
struct mtx req_mtx;
};
#define LLE_WLOCK(lle) rw_wlock(&(lle)->lle_lock)
@ -95,6 +97,12 @@ struct llentry {
#define LLE_LOCK_DESTROY(lle) rw_destroy(&(lle)->lle_lock)
#define LLE_WLOCK_ASSERT(lle) rw_assert(&(lle)->lle_lock, RA_WLOCKED)
#define LLE_REQ_INIT(lle) mtx_init(&(lle)->req_mtx, "lle req", \
NULL, MTX_DEF)
#define LLE_REQ_DESTROY(lle) mtx_destroy(&(lle)->req_mtx)
#define LLE_REQ_LOCK(lle) mtx_lock(&(lle)->req_mtx)
#define LLE_REQ_UNLOCK(lle) mtx_unlock(&(lle)->req_mtx)
#define LLE_IS_VALID(lle) (((lle) != NULL) && ((lle) != (void *)-1))
#define LLE_ADDREF(lle) do { \
@ -187,6 +195,11 @@ MALLOC_DECLARE(M_LLTABLE);
#define LLE_LINKED 0x0040 /* linked to lookup structure */
/* LLE request flags */
#define LLE_EXCLUSIVE 0x2000 /* return lle xlocked */
#define LLE_UNLOCKED 0x4000 /* return lle unlocked */
/* LLE flags used by fastpath code */
#define RLLE_VALID 0x0001 /* entry is valid */
#define RLLE_IFADDR LLE_IFADDR /* entry is ifaddr */
#define LLATBL_HASH(key, mask) \
(((((((key >> 8) ^ key) >> 8) ^ key) >> 8) ^ key) & mask)

140
sys/netinet/if_ether.c
View File

@ -78,6 +78,14 @@ static struct timeval arp_lastlog;
static int arp_curpps;
static int arp_maxpps = 1;
/* Simple ARP state machine */
enum arp_llinfo_state {
ARP_LLINFO_INCOMPLETE = 0, /* No LLE data */
ARP_LLINFO_REACHABLE, /* LLE is valid */
ARP_LLINFO_VERIFY, /* LLE is valid, need refresh */
ARP_LLINFO_DELETED, /* LLE is deleted */
};
SYSCTL_DECL(_net_link_ether);
static SYSCTL_NODE(_net_link_ether, PF_INET, inet, CTLFLAG_RW, 0, "");
static SYSCTL_NODE(_net_link_ether, PF_ARP, arp, CTLFLAG_RW, 0, "");
@ -89,6 +97,7 @@ static VNET_DEFINE(int, arp_maxtries) = 5;
static VNET_DEFINE(int, arp_proxyall) = 0;
static VNET_DEFINE(int, arpt_down) = 20; /* keep incomplete entries for
* 20 seconds */
static VNET_DEFINE(int, arpt_rexmit) = 1; /* retransmit arp entries, sec*/
VNET_PCPUSTAT_DEFINE(struct arpstat, arpstat); /* ARP statistics, see if_arp.h */
VNET_PCPUSTAT_SYSINIT(arpstat);
@ -100,6 +109,7 @@ static VNET_DEFINE(int, arp_maxhold) = 1;
#define V_arpt_keep VNET(arpt_keep)
#define V_arpt_down VNET(arpt_down)
#define V_arpt_rexmit VNET(arpt_rexmit)
#define V_arp_maxtries VNET(arp_maxtries)
#define V_arp_proxyall VNET(arp_proxyall)
#define V_arp_maxhold VNET(arp_maxhold)
@ -161,6 +171,7 @@ arptimer(void *arg)
{
struct llentry *lle = (struct llentry *)arg;
struct ifnet *ifp;
int r_skip_req;
if (lle->la_flags & LLE_STATIC) {
return;
@ -188,6 +199,55 @@ arptimer(void *arg)
ifp = lle->lle_tbl->llt_ifp;
CURVNET_SET(ifp->if_vnet);
switch (lle->ln_state) {
case ARP_LLINFO_REACHABLE:
/*
* Expiration time is approaching.
* Let's try to refresh entry if it is still
* in use.
*
* Set r_skip_req to get feedback from
* fast path. Change state and re-schedule
* ourselves.
*/
LLE_REQ_LOCK(lle);
lle->r_skip_req = 1;
LLE_REQ_UNLOCK(lle);
lle->ln_state = ARP_LLINFO_VERIFY;
callout_schedule(&lle->lle_timer, hz * V_arpt_rexmit);
LLE_WUNLOCK(lle);
CURVNET_RESTORE();
return;
case ARP_LLINFO_VERIFY:
LLE_REQ_LOCK(lle);
r_skip_req = lle->r_skip_req;
LLE_REQ_UNLOCK(lle);
if (r_skip_req == 0 && lle->la_preempt > 0) {
/* Entry was used, issue refresh request */
struct in_addr dst;
dst = lle->r_l3addr.addr4;
lle->la_preempt--;
callout_schedule(&lle->lle_timer, hz * V_arpt_rexmit);
LLE_WUNLOCK(lle);
arprequest(ifp, NULL, &dst, NULL);
CURVNET_RESTORE();
return;
}
/* Nothing happened. Reschedule if not too late */
if (lle->la_expire > time_uptime) {
callout_schedule(&lle->lle_timer, hz * V_arpt_rexmit);
LLE_WUNLOCK(lle);
CURVNET_RESTORE();
return;
}
break;
case ARP_LLINFO_INCOMPLETE:
case ARP_LLINFO_DELETED:
break;
}
if ((lle->la_flags & LLE_DELETED) == 0) {
int evt;
@ -353,26 +413,16 @@ arpresolve_full(struct ifnet *ifp, int is_gw, int create, struct mbuf *m,
if ((la->la_flags & LLE_VALID) &&
((la->la_flags & LLE_STATIC) || la->la_expire > time_uptime)) {
bcopy(&la->ll_addr, desten, ifp->if_addrlen);
renew = 0;
/*
* If entry has an expiry time and it is approaching,
* see if we need to send an ARP request within this
* arpt_down interval.
*/
if (!(la->la_flags & LLE_STATIC) &&
time_uptime + la->la_preempt > la->la_expire) {
renew = 1;
la->la_preempt--;
/* Check if we have feedback request from arptimer() */
if (la->r_skip_req != 0) {
LLE_REQ_LOCK(la);
la->r_skip_req = 0; /* Notify that entry was used */
LLE_REQ_UNLOCK(la);
}
if (pflags != NULL)
*pflags = la->la_flags;
*pflags = la->la_flags & (LLE_VALID|LLE_IFADDR);
LLE_WUNLOCK(la);
if (renew == 1)
arprequest(ifp, NULL, &SIN(dst)->sin_addr, NULL);
return (0);
}
@ -440,7 +490,7 @@ arpresolve_full(struct ifnet *ifp, int is_gw, int create, struct mbuf *m,
* m is the mbuf. May be NULL if we don't have a packet.
* dst is the next hop,
* desten is the storage to put LL address.
* flags returns lle entry flags.
* flags returns subset of lle flags: LLE_VALID | LLE_IFADDR
*
* On success, desten and flags are filled in and the function returns 0;
* If the packet must be held pending resolution, we return EWOULDBLOCK
@ -452,7 +502,6 @@ arpresolve(struct ifnet *ifp, int is_gw, struct mbuf *m,
const struct sockaddr *dst, u_char *desten, uint32_t *pflags)
{
struct llentry *la = 0;
int renew;
if (pflags != NULL)
*pflags = 0;
@ -472,40 +521,24 @@ arpresolve(struct ifnet *ifp, int is_gw, struct mbuf *m,
}
IF_AFDATA_RLOCK(ifp);
la = lla_lookup(LLTABLE(ifp), 0, dst);
IF_AFDATA_RUNLOCK(ifp);
if (la == NULL)
return (arpresolve_full(ifp, is_gw, 1, m, dst, desten, pflags));
if ((la->la_flags & LLE_VALID) &&
((la->la_flags & LLE_STATIC) || la->la_expire > time_uptime)) {
la = lla_lookup(LLTABLE(ifp), LLE_UNLOCKED, dst);
if (la != NULL && (la->r_flags & RLLE_VALID) != 0) {
/* Entry found, let's copy lle info */
bcopy(&la->ll_addr, desten, ifp->if_addrlen);
renew = 0;
/*
* If entry has an expiry time and it is approaching,
* see if we need to send an ARP request within this
* arpt_down interval.
*/
if (!(la->la_flags & LLE_STATIC) &&
time_uptime + la->la_preempt > la->la_expire) {
renew = 1;
la->la_preempt--;
}
if (pflags != NULL)
*pflags = la->la_flags;
LLE_RUNLOCK(la);
if (renew == 1)
arprequest(ifp, NULL, &SIN(dst)->sin_addr, NULL);
*pflags = LLE_VALID | (la->r_flags & RLLE_IFADDR);
/* Check if we have feedback request from arptimer() */
if (la->r_skip_req != 0) {
LLE_REQ_LOCK(la);
la->r_skip_req = 0; /* Notify that entry was used */
LLE_REQ_UNLOCK(la);
}
IF_AFDATA_RUNLOCK(ifp);
return (0);
}
LLE_RUNLOCK(la);
IF_AFDATA_RUNLOCK(ifp);
return (arpresolve_full(ifp, is_gw, 0, m, dst, desten, pflags));
return (arpresolve_full(ifp, is_gw, 1, m, dst, desten, pflags));
}
/*
@ -1042,6 +1075,9 @@ arp_check_update_lle(struct arphdr *ah, struct in_addr isaddr, struct ifnet *ifp
IF_AFDATA_WUNLOCK(ifp);
LLE_REMREF(la);
/* Clear fast path feedback request if set */
la->r_skip_req = 0;
}
arp_mark_lle_reachable(la);
@ -1073,17 +1109,21 @@ arp_check_update_lle(struct arphdr *ah, struct in_addr isaddr, struct ifnet *ifp
static void
arp_mark_lle_reachable(struct llentry *la)
{
int canceled;
int canceled, wtime;
LLE_WLOCK_ASSERT(la);
la->ln_state = ARP_LLINFO_REACHABLE;
EVENTHANDLER_INVOKE(lle_event, la, LLENTRY_RESOLVED);
if (!(la->la_flags & LLE_STATIC)) {
LLE_ADDREF(la);
la->la_expire = time_uptime + V_arpt_keep;
wtime = V_arpt_keep - V_arp_maxtries * V_arpt_rexmit;
if (wtime < 0)
wtime = V_arpt_keep;
canceled = callout_reset(&la->lle_timer,
hz * V_arpt_keep, arptimer, la);
hz * wtime, arptimer, la);
if (canceled)
LLE_REMREF(la);
}

12
sys/netinet/in.c
View File

@ -1013,6 +1013,7 @@ in_lltable_destroy_lle(struct llentry *lle)
LLE_WUNLOCK(lle);
LLE_LOCK_DESTROY(lle);
LLE_REQ_DESTROY(lle);
free(lle, M_LLTABLE);
}
@ -1034,6 +1035,7 @@ in_lltable_new(struct in_addr addr4, u_int flags)
lle->base.lle_refcnt = 1;
lle->base.lle_free = in_lltable_destroy_lle;
LLE_LOCK_INIT(&lle->base);
LLE_REQ_INIT(&lle->base);
callout_init(&lle->base.lle_timer, 1);
return (&lle->base);
@ -1257,9 +1259,12 @@ in_lltable_alloc(struct lltable *llt, u_int flags, const struct sockaddr *l3addr
return (NULL);
}
lle->la_flags = flags;
if (flags & LLE_STATIC)
lle->r_flags |= RLLE_VALID;
if ((flags & LLE_IFADDR) == LLE_IFADDR) {
lltable_set_entry_addr(ifp, lle, IF_LLADDR(ifp));
lle->la_flags |= LLE_STATIC;
lle->r_flags |= (RLLE_VALID | RLLE_IFADDR);
}
return (lle);
@ -1283,6 +1288,13 @@ in_lltable_lookup(struct lltable *llt, u_int flags, const struct sockaddr *l3add
if (lle == NULL)
return (NULL);
KASSERT((flags & (LLE_UNLOCKED|LLE_EXCLUSIVE)) !=
(LLE_UNLOCKED|LLE_EXCLUSIVE),("wrong lle request flags: 0x%X",
flags));
if (flags & LLE_UNLOCKED)
return (lle);
if (flags & LLE_EXCLUSIVE)
LLE_WLOCK(lle);
else