Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to refcount_t
From: Eric Dumazet <hidden>
Date: 2017-03-20 16:19:05
Also in:
bridge, lkml
Subsystem:
networking [general], networking [ipv4/ipv6], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, David Ahern, Ido Schimmel, Linus Torvalds
On Mon, 2017-03-20 at 07:59 -0700, Eric Dumazet wrote:
On Mon, 2017-03-20 at 07:51 -0700, Eric Dumazet wrote:quoted
atomic_cmpxchg() on PowerPC is horribly more expensive because of the added two SYNC instructions.Although I just saw that refcount was using atomic_cmpxchg_relaxed() Time to find some documentation (probably missing) or get some specs for this thing.
Interesting. UDP ipv4 xmit path gets a ~25 % improvement on PPC with this patch. ( 20 concurrent netperf -t UDP_STREAM : 2.45 Mpps -> 3.07 Mpps )
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 8471dd116771462d149e1da2807e446b69b74bcc..9f14aebf0ae1f5f366cfff0fbf58c48603916bc7 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c@@ -497,14 +497,14 @@ u32 ip_idents_reserve(u32 hash, int segs) u32 now = (u32)jiffies; u32 new, delta = 0; - if (old != now && cmpxchg(p_tstamp, old, now) == old) + if (old != now && cmpxchg_relaxed(p_tstamp, old, now) == old) delta = prandom_u32_max(now - old); /* Do not use atomic_add_return() as it makes UBSAN unhappy */ do { old = (u32)atomic_read(p_id); new = old + delta + segs; - } while (atomic_cmpxchg(p_id, old, new) != old); + } while (atomic_cmpxchg_relaxed(p_id, old, new) != old); return new - segs; }