netdev - Re: big picture UDP/IP performance question re 2.6.18 -> 2.6.32

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Date:	Mon, 03 Oct 2011 12:28:13 -0400
From:	starlight@...nacle.cx
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	linux-kernel@...r.kernel.org, netdev <netdev@...r.kernel.org>,
	Willy Tarreau <w@....eu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Stephen Hemminger <stephen.hemminger@...tta.com>
Subject: Re: big picture UDP/IP performance question re 2.6.18
  -> 2.6.32

At 06:16 PM 10/3/2011 +0200, Eric Dumazet wrote:
>> >Please send full "dmesg" output 
>> 
>> Attached.
>> 
>
>Minor note :
>
>It seems you use 4096 2MB hugepages, and your
>machine has 1GB pages availabe, you could
>try to use them.
>
>(boot cmd : hugepagesz=1GB hugepages=8 )

Interesting.  I'll give it a try for sure, but
since hugepages only gives a 5% improvement
taking the page size up probably will not
dent it by more than an additional percent
or so.

BTW I goofed on the kernel version number in my
last post.  It should be 2.6.39.4.  That .27 was
my mind transposing the 2.6.32 sub-version
onto 2.6.39.

Have one closing thought, which is to wonder if the

    9.98% swapper [kernel.kallsyms]  [k] native_safe_halt

CPU is included in the 2.6.18(rhel) CPU accounting
or not.  If it's excluded that would make 2.6.39.4
look much better--possibly put it at near parity
though I'm too lazy to do the math just now.

My guess is that this number is something of an
artifact of the clock-tick CPU histogram logic.
Perhaps it's seeing the IP register parked in the
idle-loop HALT instruction some of the time and
counting it as non-idle time.  I'd be happier if
it either counted all idle time and showed the
45% that the poll=idle run shows, or none of
the idle time at all--if it is in fact idle time.

Unfortunately 'perf' is not available for
2.6.18(rhel) so the value cannot be compared.

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