netdev - Re: Question about way that NICs deliver packets to the kernel

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Message-ID: <AANLkTi=gpPK7WEOwHV0YyAUsSLbMvhEgzw2UkuPJjNQH@mail.gmail.com>
Date:	Sun, 25 Jul 2010 22:18:40 +0800
From:	Junchang Wang <junchangwang@...il.com>
To:	Rick Jones <rick.jones2@...com>, netdev@...r.kernel.org
Cc:	Ben Hutchings <bhutchings@...arflare.com>, romieu@...zoreil.com
Subject: Re: Question about way that NICs deliver packets to the kernel

Hi list,

> Clearly something is out of joint - let's go off-list (or on to
> netperf-talk@...perf.org) and hash that out to see what may be happening.
>  It will probably involve variations on grabbing the top-of-trunk, adding
> the debug option etc.
>
The discrepancy between netperf and top has been worked out.

It seems top produce buggy data when I try to send output to a file.
For example, "top -b > output" gives out my previous buggy data in its
first iteration.

Actually, the report of top should be:

top - 21:37:15 up 21 min,  6 users,  load average: 0.43, 0.28, 0.19
Tasks: 152 total,   2 running, 149 sleeping,   0 stopped,   1 zombie
Cpu(s):  0.2%us,  5.4%sy,  0.0%ni, 50.9%id,  0.0%wa,  0.0%hi, 43.5%si,  0.0%
Mem:   2074064k total,   690192k used,  1383872k free,    39372k buffers
Swap:  2096476k total,        0k used,  2096476k free,   435056k cached

 PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
 3916 root      20   0  2228  584  296 R 86.3  0.0   0:09.72 netserver

I think 50.9% system idle makes sense because this is a dual-core system
and netserver is consuming 86.3% of a core. On average, the CPU usage
of the whole system reported by top can be regarded as from 46.2% to
50.1%.

netperf's report of 48% is right and testifies that "there is no huge
discrepancy
between the overall CPU utilization reported by top and the CPU utilization
reported by netperf."

Thanks Rick.

-- 
--Junchang
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