It speeds up route cache lookup by 30-50% approximately as measured
with synthetic benchmark suggested by Dave.
http://marc.theaimsgroup.com/?l=linux-kernel&m=102258603404836&w=2
The entire discussion is in -
http://marc.theaimsgroup.com/?t=102258611100001&r=1&w=2
Thanks
-- Dipankar Sarma <dipankar@in.ibm.com> http://lse.sourceforge.net Linux Technology Center, IBM Software Lab, Bangalore, India.rt_rcu-2.5.43-1.patch ---------------------
diff -urN linux-2.5.43-base/include/net/dst.h linux-2.5.43-rt_rcu/include/net/dst.h --- linux-2.5.43-base/include/net/dst.h Wed Oct 16 08:59:04 2002 +++ linux-2.5.43-rt_rcu/include/net/dst.h Sat Oct 19 03:25:26 2002 @@ -9,6 +9,7 @@ #define _NET_DST_H #include <linux/config.h> +#include <linux/rcupdate.h> #include <net/neighbour.h> /* @@ -62,6 +63,7 @@ #endif struct dst_ops *ops; + struct rcu_head rcu_head; char info[0]; }; diff -urN linux-2.5.43-base/net/ipv4/route.c linux-2.5.43-rt_rcu/net/ipv4/route.c --- linux-2.5.43-base/net/ipv4/route.c Wed Oct 16 08:59:06 2002 +++ linux-2.5.43-rt_rcu/net/ipv4/route.c Sat Oct 19 04:05:16 2002 @@ -85,6 +85,7 @@ #include <linux/mroute.h> #include <linux/netfilter_ipv4.h> #include <linux/random.h> +#include <linux/rcupdate.h> #include <net/protocol.h> #include <net/ip.h> #include <net/route.h> @@ -188,7 +189,7 @@ struct rt_hash_bucket { struct rtable *chain; - rwlock_t lock; + spinlock_t lock; } __attribute__((__aligned__(8))); static struct rt_hash_bucket *rt_hash_table; @@ -226,8 +227,8 @@ len = 128; } + rcu_read_lock(); for (i = rt_hash_mask; i >= 0; i--) { - read_lock_bh(&rt_hash_table[i].lock); for (r = rt_hash_table[i].chain; r; r = r->u.rt_next) { /* * Spin through entries until we are ready @@ -238,6 +239,7 @@ len = 0; continue; } + read_barrier_depends(); sprintf(temp, "%s\t%08lX\t%08lX\t%8X\t%d\t%u\t%d\t" "%08lX\t%d\t%u\t%u\t%02X\t%d\t%1d\t%08X", r->u.dst.dev ? r->u.dst.dev->name : "*", @@ -262,14 +264,13 @@ sprintf(buffer + len, "%-127s\n", temp); len += 128; if (pos >= offset+length) { - read_unlock_bh(&rt_hash_table[i].lock); goto done; } } - read_unlock_bh(&rt_hash_table[i].lock); } done: + rcu_read_unlock(); *start = buffer + len - (pos - offset); len = pos - offset; if (len > length) @@ -318,13 +319,13 @@ static __inline__ void rt_free(struct rtable *rt) { - dst_free(&rt->u.dst); + call_rcu(&rt->u.dst.rcu_head, (void (*)(void *))dst_free, &rt->u.dst); } static __inline__ void rt_drop(struct rtable *rt) { ip_rt_put(rt); - dst_free(&rt->u.dst); + call_rcu(&rt->u.dst.rcu_head, (void (*)(void *))dst_free, &rt->u.dst); } static __inline__ int rt_fast_clean(struct rtable *rth) @@ -377,7 +378,7 @@ i = (i + 1) & rt_hash_mask; rthp = &rt_hash_table[i].chain; - write_lock(&rt_hash_table[i].lock); + spin_lock(&rt_hash_table[i].lock); while ((rth = *rthp) != NULL) { if (rth->u.dst.expires) { /* Entry is expired even if it is in use */ @@ -396,7 +397,7 @@ *rthp = rth->u.rt_next; rt_free(rth); } - write_unlock(&rt_hash_table[i].lock); + spin_unlock(&rt_hash_table[i].lock); /* Fallback loop breaker. */ if ((jiffies - now) > 0) @@ -419,11 +420,11 @@ rt_deadline = 0; for (i = rt_hash_mask; i >= 0; i--) { - write_lock_bh(&rt_hash_table[i].lock); + spin_lock_bh(&rt_hash_table[i].lock); rth = rt_hash_table[i].chain; if (rth) rt_hash_table[i].chain = NULL; - write_unlock_bh(&rt_hash_table[i].lock); + spin_unlock_bh(&rt_hash_table[i].lock); for (; rth; rth = next) { next = rth->u.rt_next; @@ -547,7 +548,7 @@ k = (k + 1) & rt_hash_mask; rthp = &rt_hash_table[k].chain; - write_lock_bh(&rt_hash_table[k].lock); + spin_lock_bh(&rt_hash_table[k].lock); while ((rth = *rthp) != NULL) { if (!rt_may_expire(rth, tmo, expire)) { tmo >>= 1; @@ -558,7 +559,7 @@ rt_free(rth); goal--; } - write_unlock_bh(&rt_hash_table[k].lock); + spin_unlock_bh(&rt_hash_table[k].lock); if (goal <= 0) break; } @@ -619,7 +620,7 @@ restart: rthp = &rt_hash_table[hash].chain; - write_lock_bh(&rt_hash_table[hash].lock); + spin_lock_bh(&rt_hash_table[hash].lock); while ((rth = *rthp) != NULL) { if (memcmp(&rth->fl, &rt->fl, sizeof(rt->fl)) == 0) { /* Put it first */ @@ -630,7 +631,7 @@ rth->u.dst.__use++; dst_hold(&rth->u.dst); rth->u.dst.lastuse = now; - write_unlock_bh(&rt_hash_table[hash].lock); + spin_unlock_bh(&rt_hash_table[hash].lock); rt_drop(rt); *rp = rth; @@ -646,7 +647,7 @@ if (rt->rt_type == RTN_UNICAST || rt->fl.iif == 0) { int err = arp_bind_neighbour(&rt->u.dst); if (err) { - write_unlock_bh(&rt_hash_table[hash].lock); + spin_unlock_bh(&rt_hash_table[hash].lock); if (err != -ENOBUFS) { rt_drop(rt); @@ -687,7 +688,7 @@ } #endif rt_hash_table[hash].chain = rt; - write_unlock_bh(&rt_hash_table[hash].lock); + spin_unlock_bh(&rt_hash_table[hash].lock); *rp = rt; return 0; } @@ -754,7 +755,7 @@ { struct rtable **rthp; - write_lock_bh(&rt_hash_table[hash].lock); + spin_lock_bh(&rt_hash_table[hash].lock); ip_rt_put(rt); for (rthp = &rt_hash_table[hash].chain; *rthp; rthp = &(*rthp)->u.rt_next) @@ -763,7 +764,7 @@ rt_free(rt); break; } - write_unlock_bh(&rt_hash_table[hash].lock); + spin_unlock_bh(&rt_hash_table[hash].lock); } void ip_rt_redirect(u32 old_gw, u32 daddr, u32 new_gw, @@ -802,10 +803,11 @@ rthp=&rt_hash_table[hash].chain; - read_lock(&rt_hash_table[hash].lock); + rcu_read_lock(); while ((rth = *rthp) != NULL) { struct rtable *rt; + read_barrier_depends(); if (rth->fl.fl4_dst != daddr || rth->fl.fl4_src != skeys[i] || rth->fl.fl4_tos != tos || @@ -823,7 +825,7 @@ break; dst_clone(&rth->u.dst); - read_unlock(&rt_hash_table[hash].lock); + rcu_read_unlock(); rt = dst_alloc(&ipv4_dst_ops); if (rt == NULL) { @@ -834,6 +836,7 @@ /* Copy all the information. */ *rt = *rth; + INIT_RCU_HEAD(&rt->u.dst.rcu_head); rt->u.dst.__use = 1; atomic_set(&rt->u.dst.__refcnt, 1); if (rt->u.dst.dev) @@ -869,7 +872,7 @@ ip_rt_put(rt); goto do_next; } - read_unlock(&rt_hash_table[hash].lock); + rcu_read_unlock(); do_next: ; } @@ -1049,9 +1052,10 @@ for (i = 0; i < 2; i++) { unsigned hash = rt_hash_code(daddr, skeys[i], tos); - read_lock(&rt_hash_table[hash].lock); + rcu_read_lock(); for (rth = rt_hash_table[hash].chain; rth; rth = rth->u.rt_next) { + read_barrier_depends(); if (rth->fl.fl4_dst == daddr && rth->fl.fl4_src == skeys[i] && rth->rt_dst == daddr && @@ -1087,7 +1091,7 @@ } } } - read_unlock(&rt_hash_table[hash].lock); + rcu_read_unlock(); } return est_mtu ? : new_mtu; } @@ -1639,8 +1643,9 @@ tos &= IPTOS_RT_MASK; hash = rt_hash_code(daddr, saddr ^ (iif << 5), tos); - read_lock(&rt_hash_table[hash].lock); + rcu_read_lock(); for (rth = rt_hash_table[hash].chain; rth; rth = rth->u.rt_next) { + read_barrier_depends(); if (rth->fl.fl4_dst == daddr && rth->fl.fl4_src == saddr && rth->fl.iif == iif && @@ -1653,12 +1658,12 @@ dst_hold(&rth->u.dst); rth->u.dst.__use++; rt_cache_stat[smp_processor_id()].in_hit++; - read_unlock(&rt_hash_table[hash].lock); + rcu_read_unlock(); skb->dst = (struct dst_entry*)rth; return 0; } } - read_unlock(&rt_hash_table[hash].lock); + rcu_read_unlock(); /* Multicast recognition logic is moved from route cache to here. The problem was that too many Ethernet cards have broken/missing @@ -1998,8 +2003,9 @@ hash = rt_hash_code(flp->fl4_dst, flp->fl4_src ^ (flp->oif << 5), flp->fl4_tos); - read_lock_bh(&rt_hash_table[hash].lock); + rcu_read_lock(); for (rth = rt_hash_table[hash].chain; rth; rth = rth->u.rt_next) { + read_barrier_depends(); if (rth->fl.fl4_dst == flp->fl4_dst && rth->fl.fl4_src == flp->fl4_src && rth->fl.iif == 0 && @@ -2013,12 +2019,12 @@ dst_hold(&rth->u.dst); rth->u.dst.__use++; rt_cache_stat[smp_processor_id()].out_hit++; - read_unlock_bh(&rt_hash_table[hash].lock); + rcu_read_unlock(); *rp = rth; return 0; } } - read_unlock_bh(&rt_hash_table[hash].lock); + rcu_read_unlock(); return ip_route_output_slow(rp, flp); } @@ -2208,9 +2214,10 @@ if (h < s_h) continue; if (h > s_h) s_idx = 0; - read_lock_bh(&rt_hash_table[h].lock); + rcu_read_lock(); for (rt = rt_hash_table[h].chain, idx = 0; rt; rt = rt->u.rt_next, idx++) { + read_barrier_depends(); if (idx < s_idx) continue; skb->dst = dst_clone(&rt->u.dst); @@ -2218,12 +2225,12 @@ cb->nlh->nlmsg_seq, RTM_NEWROUTE, 1) <= 0) { dst_release(xchg(&skb->dst, NULL)); - read_unlock_bh(&rt_hash_table[h].lock); + rcu_read_unlock(); goto done; } dst_release(xchg(&skb->dst, NULL)); } - read_unlock_bh(&rt_hash_table[h].lock); + rcu_read_unlock(); } done: @@ -2505,7 +2512,7 @@ rt_hash_mask--; for (i = 0; i <= rt_hash_mask; i++) { - rt_hash_table[i].lock = RW_LOCK_UNLOCKED; + rt_hash_table[i].lock = SPIN_LOCK_UNLOCKED; rt_hash_table[i].chain = NULL; } - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/