From: Stephen Hemminger <stephen@networkplumber.org>
To: George Prekas <prekageo@amazon.com>
Cc: Wenzhuo Lu <wenzhuo.lu@intel.com>,
Beilei Xing <beilei.xing@intel.com>,
Bernard Iremonger <bernard.iremonger@intel.com>, <dev@dpdk.org>
Subject: Re: [dpdk-dev] [PATCH] app/testpmd: fix IP checksum calculation
Date: Thu, 3 Dec 2020 10:33:05 -0800 [thread overview]
Message-ID: <20201203103305.568f14c3@hermes.local> (raw)
In-Reply-To: <56967649-1494-aacf-ce65-9df575233b86@amazon.com>
On Thu, 3 Dec 2020 10:35:50 -0600
George Prekas <prekageo@amazon.com> wrote:
> On 12/3/2020 10:08 AM, Stephen Hemminger wrote:
> > On Thu, 3 Dec 2020 07:59:54 -0600
> > George Prekas <prekageo@amazon.com> wrote:
> >
> >> Insert a compiler barrier to make sure that the IP checksum calculation
> >> happens after setting all the fields of the IP header.
> >>
> >> Signed-off-by: George Prekas <prekageo@amazon.com>
> > I don't think this is necessary. All other OS's don't have to do this.
> > The CPU is going to maintain proper memory order.
>
> Hi Stephen,
>
> This is not a CPU or OS issue. This is a compiler issue. The compiler is
> free to reorder statements if it does not detect dependencies between
> them. Without this compiler barrier, the calculated IP checksum is wrong.
>
>
But the compiler should be detecting any aliasing here, if no you have
a bad compiler.
next prev parent reply other threads:[~2020-12-03 18:33 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-03 13:59 [dpdk-dev] [PATCH] app/testpmd: fix IP checksum calculation George Prekas
2020-12-03 16:08 ` Stephen Hemminger
2020-12-03 16:35 ` George Prekas
2020-12-03 18:33 ` Stephen Hemminger [this message]
2020-12-04 8:59 ` Ferruh Yigit
2020-12-05 5:47 ` George Prekas
2020-12-05 5:42 ` [dpdk-dev] [PATCH v2] " George Prekas
2021-01-05 16:26 ` George Prekas
2021-01-06 18:02 ` Ferruh Yigit
2021-01-07 5:25 ` Stephen Hemminger
2021-01-07 5:39 ` George Prekas
2021-01-07 11:32 ` Ferruh Yigit
2021-01-07 13:06 ` Ferruh Yigit
2021-01-07 14:20 ` George Prekas
2021-01-07 15:22 ` Ferruh Yigit
2021-01-07 20:45 ` George Prekas
2021-01-07 15:50 ` Stephen Hemminger
2021-01-07 15:59 ` Ferruh Yigit
2021-01-07 16:29 ` Stephen Hemminger
2021-01-07 20:42 ` [dpdk-dev] [PATCH v3] " George Prekas
2021-01-18 15:20 ` Ferruh Yigit
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