linux-kernel - Re: [PATCH] x86: Run checksumming in parallel accross multiple alu's

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Message-ID: <1381847168.2045.45.camel@edumazet-glaptop.roam.corp.google.com>
Date:	Tue, 15 Oct 2013 07:26:08 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Sébastien Dugué <sebastien.dugue@...l.net>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Neil Horman <nhorman@...driver.com>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Subject: Re: [PATCH] x86: Run checksumming in parallel accross multiple alu's

On Tue, 2013-10-15 at 16:15 +0200, Sébastien Dugué wrote:
> Hi Eric,
> 
> On Tue, 15 Oct 2013 07:06:25 -0700
> Eric Dumazet <eric.dumazet@...il.com> wrote:

> > But the csum cost is both for sender and receiver ?
> 
>   No, it was only on the receiver side that I noticed it.
> 

Yes, as Andi said, we do the csum while copying the data for the
sender : (I disabled hardware assist tx checksum using 'ethtool -K eth0
tx off')

    17.21%  netperf  [kernel.kallsyms]       [k]
csum_partial_copy_generic                 
            |
            --- csum_partial_copy_generic
               |          
               |--97.39%-- __libc_send
               |          
                --2.61%-- tcp_sendmsg
                          inet_sendmsg
                          sock_sendmsg
                          _sys_sendto
                          sys_sendto
                          system_call_fastpath
                          __libc_send



>   Sorry, but this is 3 years old stuff and I do not have the
> setup anymore to reproduce.

And the receiver should also do the same : (ethtool -K eth0 rx off)

    10.55%    netserver  [kernel.kallsyms]  [k]
csum_partial_copy_generic            
              |
              --- csum_partial_copy_generic
                 |          
                 |--98.24%-- __libc_recv
                 |          
                  --1.76%-- skb_copy_and_csum_datagram
                            skb_copy_and_csum_datagram_iovec
                            tcp_rcv_established
                            tcp_v4_do_rcv
                            |          
                            |--73.05%-- tcp_prequeue_process
                            |          tcp_recvmsg
                            |          inet_recvmsg
                            |          sock_recvmsg
                            |          SYSC_recvfrom
                            |          SyS_recvfrom
                            |          system_call_fastpath
                            |          __libc_recv
                            |          

So I suspect something is wrong with IPoIB.




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