We are planning to deploy a system for a client. I was told that
leaving unnecessary modules (ie. jfs, usb, etc...) will not cause
latencies in the kernel however the client is very sensitive.  They
care about latencies in microseconds and I was wondering if leaving
unnecessary modules loaded would cause it and how can I measure the
kernel latency (with lmbench if possible) w/o necessary modules.

TIA

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Hi...



if you just "leave" them, it wouldn't add any overhead IMHO. Only if
it is loaded. For that, you could either blacklist them or
better....deselect them during kernel config. Whichever suits you
better

PS: If you're really sensitive, perhaps you could make all of your
modules build into the kernel image...therefore there won't be any

what latency are we talking here? scheduling latency?

-- 
regards,

Mulyadi Santosa
Freelance Linux trainer and consultant

blog: the-hydra.blogspot.com
training: mulyaditraining.blogspot.com

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I am talking about scheduling latency and more important  network latency

On Mon, Jan 3, 2011 at 3:06 PM, Mulyadi Santosa

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Hi..


Please don't do top posting....

About measuring latency, I think you can use lmbench along with ftrace
(check http://lxr.linux.no/linux+*/Documentation/trace/events.txt for
the details). Uhm and I think you could probably use the new "perf"
tool, which is bundled in vanilla kernel tarball.

Network latency? Perhaps you can check this article "Benchmarking
network  performance with Network Pipemeter, LMbench, and nuttcp"
(http://www.linux.com/archive/feature/144532)

All in all, the things that might affect the latency stuffs IMHO are:
all tracing related functionality, traffic filtering/shaping, security
modules. even if they were indeed loaded, I think the overhead might
be negligible if you use them carefully and properly.

-- 
regards,

Mulyadi Santosa
Freelance Linux trainer and consultant

blog: the-hydra.blogspot.com
training: mulyaditraining.blogspot.com

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