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Date: Fri, 01 May 2015 10:37:49 -0700 From: Eric Dumazet <eric.dumazet@...il.com> To: David Miller <davem@...emloft.net> Cc: netdev <netdev@...r.kernel.org> Subject: [PATCH net-next] ipv4: speedup ip_idents_reserve() From: Eric Dumazet <edumazet@...gle.com> Under stress, ip_idents_reserve() is accessing a contended cache line twice, with non optimal MESI transactions. If we place timestamps in separate location, we reduce this pressure by ~50% and allow atomic_add_return() to issue a Request for Ownership. Signed-off-by: Eric Dumazet <edumazet@...gle.com> --- net/ipv4/route.c | 20 +++++++++++--------- 1 file changed, 11 insertions(+), 9 deletions(-) diff --git a/net/ipv4/route.c b/net/ipv4/route.c index a78540f28276..f7559cba4343 100644 --- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -457,12 +457,9 @@ static struct neighbour *ipv4_neigh_lookup(const struct dst_entry *dst, } #define IP_IDENTS_SZ 2048u -struct ip_ident_bucket { - atomic_t id; - u32 stamp32; -}; -static struct ip_ident_bucket *ip_idents __read_mostly; +static atomic_t *ip_idents __read_mostly; +static u32 *ip_tstamps __read_mostly; /* In order to protect privacy, we add a perturbation to identifiers * if one generator is seldom used. This makes hard for an attacker @@ -470,15 +467,16 @@ static struct ip_ident_bucket *ip_idents __read_mostly; */ u32 ip_idents_reserve(u32 hash, int segs) { - struct ip_ident_bucket *bucket = ip_idents + hash % IP_IDENTS_SZ; - u32 old = ACCESS_ONCE(bucket->stamp32); + u32 *p_tstamp = ip_tstamps + hash % IP_IDENTS_SZ; + atomic_t *p_id = ip_idents + hash % IP_IDENTS_SZ; + u32 old = ACCESS_ONCE(*p_tstamp); u32 now = (u32)jiffies; u32 delta = 0; - if (old != now && cmpxchg(&bucket->stamp32, old, now) == old) + if (old != now && cmpxchg(p_tstamp, old, now) == old) delta = prandom_u32_max(now - old); - return atomic_add_return(segs + delta, &bucket->id) - segs; + return atomic_add_return(segs + delta, p_id) - segs; } EXPORT_SYMBOL(ip_idents_reserve); @@ -2741,6 +2739,10 @@ int __init ip_rt_init(void) prandom_bytes(ip_idents, IP_IDENTS_SZ * sizeof(*ip_idents)); + ip_tstamps = kcalloc(IP_IDENTS_SZ, sizeof(*ip_tstamps), GFP_KERNEL); + if (!ip_tstamps) + panic("IP: failed to allocate ip_tstamps\n"); + for_each_possible_cpu(cpu) { struct uncached_list *ul = &per_cpu(rt_uncached_list, cpu); -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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