netdev - Re: [PATCH net-next] udp: use sk_protocol instead of pcflag to detect udplite sockets

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Message-ID: <1490973841.8750.26.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Fri, 31 Mar 2017 08:24:01 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     Paolo Abeni <pabeni@...hat.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH net-next] udp: use sk_protocol instead of pcflag to
 detect udplite sockets

On Fri, 2017-03-31 at 15:03 +0000, David Laight wrote:

> Is that really sensible on systems with large cache lines?

Yes it is.

We mostly do our perf analysis on x86, and it turns out that linux
networking on PowerPC is not great because of this.

struct dst_entry is showing problems, simply because we aligned __refcnt
on 64 byte boundary, which is not enough on PowerPC.

With bigger cache lines, you have bigger chances of false sharing.