Re: bash performance
On Mon, 2010-10-25 at 23:31 +0300, Tarko Tikan wrote:
> hey,
>
> This is a fresh squeeze install on T5220 (same for the laptop I'm comparing with). Whole machine seems strangely slow but one thing I can point out for sure is bash. I've been debugging this issue for a week now (even comparing strace -ttt time outputs with random intel machine). Does this seem strange to anyone else?:
>
> randomx86laptop$ time (VAR=0; for i in `seq 0 99999`; do let VAR=VAR+i; done)
> real 0m1.235s
> user 0m1.212s
> sys 0m0.036s
>
> niagara2$ time (VAR=0; for i in `seq 0 99999`; do let VAR=VAR+i; done)
> real 0m11.193s
> user 0m10.777s
> sys 0m0.388s
>
> I first noticed this with bash_completion - every new bash instance takes 2-3 seconds to start.
>
> Anyone have an idea whats going on?
Can you give us a bit more info about the laptop? IIRC a T5220 runs an
UltraSPARC T2 at about 1Ghz. These are designed for throughput, not
latency. The T2 is out of order but only 2 way dispatch (IIRC),
compared to a 3.4Ghz Intel chip with 4 way dispatch and full out of
order instruction completion. Thus in terms of single threaded
performance, I'm not exactly surprised an x86 laptop is 'faster'. A
factor of 10 seems a bit steep but 3-4 maybe 5 times I could believe.
However if you look at performance of code that is tightly branching,
memory latency/bandwidth sensitive or thread interaction critical, you
should see scaling up to .. well ... it depends on the app but I've seen
near linear speed up, up to 32 threads on T1s.
What other benchmarks have you tried? Also have you tried with any
other OS (i.e. Open Solaris) on the same hardware; this should rule out
anything Debian / Linux specific. Likewise have you tried other
machines?
Cheers,
- Martin
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