From: Andi Kleen <andi@firstfloor•org>
To: "\"Oleg A. Arkhangelsky\"" <sysoleg@yandex•ru>
Cc: linux-perf-users@vger•kernel.org, netdev@vger•kernel.org
Subject: Re: Inconsistent perf top output
Date: Sun, 06 Apr 2014 21:10:34 -0700 [thread overview]
Message-ID: <87ioqlkced.fsf@tassilo.jf.intel.com> (raw)
In-Reply-To: <645781396449095@web21h.yandex.ru> (Oleg A. Arkhangelsky's message of "Wed, 02 Apr 2014 18:31:35 +0400")
"\"Oleg A. Arkhangelsky\"" <sysoleg@yandex•ru> writes:
Better asked on netdev. Copied here. It's unlikely to be a perf problem.
You better specify what kernel version you have.
> Hello,
>
> I'm profiling Linux IP packet forwarding performance. In common case I see this
> functions eating most of CPU cycles.
>
> 13735.00 22.5% build_skb
> 5138.00 8.4% ipt_do_table
> 4750.00 7.8% fib_table_lookup
> 3519.00 5.8% ixgbe_clean_rx_irq
> 2836.00 4.6% nf_iterate
> 1530.00 2.5% dev_queue_xmit
>
> Looks good. But accidentally I run tcpdump program on one of the NICs related
> to my test. After killing tcpdump I see that top is different:
>
> 6362.00 10.3% fib_table_lookup
> 6227.00 10.1% ipt_do_table
> 4300.00 7.0% ixgbe_clean_rx_irq
> 3771.00 6.1% nf_iterate
> 3284.00 5.3% build_skb
> 2179.00 3.5% ixgbe_xmit_frame_ring
>
> Dramatic change in build_skb() cpu cycles. But tcpdump is not active anymore.
> More than this, if I stop pktgen on traffic generator PC for a few seconds and
> start it again without any other changes, I see that build_skb() is top offender
> again. Running tcpdump again and killing it move fib_table_lookup() or
> ipt_do_table() (they are pretty same in cpu cycles) to the top. So this behavior
> is reproducible.
>
> I just have no sane explanation to such strange behavior. Maybe someone have?
>
> Thank you!
--
ak@linux•intel.com -- Speaking for myself only
parent reply other threads:[~2014-04-07 4:10 UTC|newest]
Thread overview: expand[flat|nested] mbox.gz Atom feed
[parent not found: <645781396449095@web21h.yandex.ru>]
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