linux-kernel - Re: -27% netperf TCP_STREAM regression by "tcp_memcontrol: Kill struct tcp

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Date:	Wed, 23 Oct 2013 14:25:43 +0200
From:	Christoph Paasch <christoph.paasch@...ouvain.be>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	David Miller <davem@...emloft.net>, fengguang.wu@...el.com,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: -27% netperf TCP_STREAM regression by "tcp_memcontrol: Kill
 struct tcp_memcontrol"

Hello,

On 22/10/13 - 21:38:10, Eric W. Biederman wrote:
> David Miller <davem@...emloft.net> writes:
> > From: fengguang.wu@...el.com
> > Date: Tue, 22 Oct 2013 22:41:29 +0100
> >
> >> We noticed big netperf throughput regressions
> >> 
> >>     a4fe34bf902b8f709c63      2e685cad57906e19add7  
> >> ------------------------  ------------------------  
> >>                   707.40       -40.7%       419.60  lkp-nex04/micro/netperf/120s-200%-TCP_STREAM
> >>                  2775.60       -23.7%      2116.40  lkp-sb03/micro/netperf/120s-200%-TCP_STREAM
> >>                  3483.00       -27.2%      2536.00  TOTAL netperf.Throughput_Mbps
> >> 
> >> and bisected it to
> >> 
> >> commit 2e685cad57906e19add7189b5ff49dfb6aaa21d3
> >> Author: Eric W. Biederman <ebiederm@...ssion.com>
> >> Date:   Sat Oct 19 16:26:19 2013 -0700
> >> 
> >>     tcp_memcontrol: Kill struct tcp_memcontrol
> >
> > Eric please look into this, I'd rather have a fix to apply than revert your
> > work.
> 
> Will do I expect some ordering changed, and that changed the cache line
> behavior.

may it be the below?


Cheers,
Christoph

----
From: Christoph Paasch <christoph.paasch@...ouvain.be>
Subject: [PATCH] Fix: Dereference pointer-value of sk_prot->memory_pressure

2e685cad57 (tcp_memcontrol: Kill struct tcp_memcontrol) falsly modified
the access to memory_pressure of sk->sk_prot->memory_pressure. The patch
did modify the memory_pressure-field of struct cg_proto, but not the one
of struct proto.

So, the access to sk_prot->memory_pressure should not be changed.

Reported-by: Fengguang Wu <fengguang.wu@...el.com>
Signed-off-by: Christoph Paasch <christoph.paasch@...ouvain.be>
---
 include/net/sock.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/net/sock.h b/include/net/sock.h
index c93542f..e3a18ff 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1137,7 +1137,7 @@ static inline bool sk_under_memory_pressure(const struct sock *sk)
        if (mem_cgroup_sockets_enabled && sk->sk_cgrp)
                return !!sk->sk_cgrp->memory_pressure;

-       return !!sk->sk_prot->memory_pressure;
+       return !!*sk->sk_prot->memory_pressure;
 }

 static inline void sk_leave_memory_pressure(struct sock *sk)
-- 
1.8.3.2


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