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Date:      Sun, 23 Apr 2006 19:27:35 -0700
From:      Don Dugger <dugger@hotlz.com>
To:        freebsd-chat@freebsd.org
Cc:        Benjamin Lutz <benlutz@datacomm.ch>, Dan Strick <strick@covad.net>
Subject:   Re: Why is not more FreeBSD software written in C++?
Message-ID:  <444C3797.7010909@hotlz.com>
In-Reply-To: <200604232232.32653.benlutz@datacomm.ch>
References:  <200604231525.k3NFP64X003155@mist.nodomain> <200604232232.32653.benlutz@datacomm.ch>

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For fun I run the tests on a SUN box I have here it's an old Sparc 
200MHz Running Solaris 8.
and I used the gcc 3.4.2 compiler.

----------
time ./test_putchar >/dev/null

real    0m0.45s
user    0m0.44s
sys     0m0.01s

time ./test_write >/dev/null

real    0m0.66s
user    0m0.38s
sys     0m0.28s

time ./test_iostream >/dev/null

real    0m3.28s
user    0m3.12s
sys     0m0.04s

time ./test_string >/dev/null

real    0m1.50s
user    0m1.48s
sys     0m0.02s

----------

Don 8)

Benjamin Lutz wrote:
> Hello Dan,
>
> On Sunday 23 April 2006 17:25, Dan Strick wrote:
>   
>> My results show something quite different.  Even though the buffer
>> size used by Benjamin's write() test (61 bytes) is much larger than
>> the one I used (only 24 bytes), the write() test to /dev/null still
>> takes about 4 times longer than the putchar() test.  As one might
>> expect, the write() test spends most of its time in the kernel doing
>> all those write() system calls.  The putchar() test (i.e. stdio)
>> is probably using a 1K byte buffer.
>>     
>
> Your results are intriguing. I ran the tests again on a FreeBSD-6 machine (A 
> Sempron 3000+), and I see the same thing, test_putchar runs faster and with 
> much lower cpu load than test_write.
>
> I'm not sure what to make of this. I would have said that the reason that 
> write() is faster is because there's much fewer kernel calls necessary. I'm 
> beginning to think though that FreeBSD's write(2) implementation is not as 
> good as it could be. My Linux Mac Mini using a notebook HD actually runs 
> test_write 10% faster than the FreeBSD Sempron 3000+ using proper SATA disks.
>
> Or maybe Linux just cheats by doing some smart delaying/caching.
>
> Thinking about it some more, I think you're right with your assumption that 
> test_putchar is faster because stdio does some internal buffering. I ran 
> ktrace on test_putchar (the version with 500'000 lines), and it calls write() 
> 4562 times on said FreeBSD system, each time with 0x1000 as last argument, ie 
> it uses 4KB buffers. To confirm that buffering to be the reason, I increased 
> the size of each line from 61 bytes to 16001 bytes, at which point the 
> write() version showed a clear performance advantage on FreeBSD as well.
>
> I had not thought about this possibility when I made my original statement. 
> Given that, it makes sense that putchar is quite fast.
>
> It still puzzles me though why the Mini (it's only a 1.25GHz G4!) beats the 
> Sempron though.
>
>   
>> I stand by my suggestion that using putchar() might not be slower.
>> On my system it was much faster.
>>     
>
> Ok, I accept that then. If we think of a case where buffering must not happen, 
> and thus a putchar() must be followed by a fflush(), would you agree that 
> just using write() is faster?
>
> Cheers
> Benjamin
>   




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