[CentOS] scheduling differences between CentOS 4 and CentOS 5?
R P Herrold
herrold at owlriver.com
Tue May 24 18:22:12 UTC 2011
On Mon, 23 May 2011, Mag Gam wrote:
> I would like to confirm Matt's claim. I too experienced larger
> latencies with Centos 5.x compared to 4.x. My application is very
> network sensitive and its easy to prove using lat_tcp.
> Russ,
> I am curious about identifying the problem. What tools do you
> recommend to find where the latency is coming from in the application?
I went through the obvious candidates:
system calls
(loss of control of when if ever the
scheduler decides to let your process run again)
polling v select
polling is almost always a wrong approach when
latency reduction is in play
(reading and understanding: man 2 select_tut
is time very well spent)
choice of implementation language -- the issue here
being if one uses a scripting language, one cannot
'see' the time leaks
Doing metrics permits both 'hot spot' analysis, and moves the
coding from 'guesstimation' to software engineering. We use
graphviz, and gnuplot on the plain text 'CSV-style' timings
files to 'see' outliers and hotspots
Knuth's admonition about premature optimization applies here
of course
A sensible process might be:
Make it work correctly, THEN make it fast
Some people add a precursor step of:
make it compile
but this seems to me a less efficient process than simply
proceeding up with a clean design at the start, and the
expedient of 'stubbing' out unimplemented portions. Then
replace the stubs with 'correctly' funcitoning refactorings
(... I just did this with part of my build tools, writing a
meta-code outline of what I wanted, and then implementing the
metacode)
The C++ code of the 'trading-shim' tool (GPLv3+) was produced
in just this fashion over the last few years, and compared to
all the competitors in its class, outpaces them all in terms
of minimal latency .. most of that competition being Java
based, or in some other scripting language. The 'shim' runs
like a scalded dog ;)
-- Russ herrold
More information about the CentOS
mailing list