writev() and other myths...
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Feb. 12th, 2008 | 06:53 pm
I've been looking from different angles on ways to make memcached_get() (aka from libmemcached) faster.
I keep toying with different ideas... rewriting it in different ways to see if I can get any performance changes in it.
Thus far... nada... no go.
Yesterday I had the idea of "bypass my write buffer, use writev() to push the data to the client".
This would save me in design two memory copies.
Results?
writev() was slower.
D'oh!
What to do, what to do...
I keep a copy of glibc() on my laptop. I do this for just such the occasion.
How is writev() implemented? It alloc's memory large enough to contain the data, does a copy, and then calls write().
Well crap.
I have never used writev() before, the interface has just never been one I wanted to deal with for asynchronous connections.
I had always assumed that it was clever. Somehow saving on system calls, yadda, yadda, yadda...
Nope, it does not.
Oh well :)
Back to the drawing board...
I keep toying with different ideas... rewriting it in different ways to see if I can get any performance changes in it.
Thus far... nada... no go.
Yesterday I had the idea of "bypass my write buffer, use writev() to push the data to the client".
This would save me in design two memory copies.
Results?
writev() was slower.
D'oh!
What to do, what to do...
I keep a copy of glibc() on my laptop. I do this for just such the occasion.
How is writev() implemented? It alloc's memory large enough to contain the data, does a copy, and then calls write().
Well crap.
I have never used writev() before, the interface has just never been one I wanted to deal with for asynchronous connections.
I had always assumed that it was clever. Somehow saving on system calls, yadda, yadda, yadda...
Nope, it does not.
Oh well :)
Back to the drawing board...
Not true, libc is just confusing
from:
illiterat
date: Feb. 13th, 2008 06:36 am (UTC)
Link
sysdeps/unix/sysv/linux/writev.c
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Re: Not true, libc is just confusing
from:
krow
date: Feb. 13th, 2008 11:49 am (UTC)
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I also dislike how write partial failures work. Since you have to calculate into the structure to find out where you should startup again.
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Why not just use mmap()
from:
markxr
date: Feb. 13th, 2008 09:45 am (UTC)
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It should be more efficient. Please consider it :)
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Re: Why not just use mmap()
from:
krow
date: Feb. 13th, 2008 11:44 am (UTC)
Link
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Re: Why not just use mmap()
from:
markxr
date: Feb. 13th, 2008 12:46 pm (UTC)
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Have you considered doing the system calls anyway, but using the TCP_CORK linux-specific option to get the kernel to buffer it until your packet is complete? I am not sure whether this would be helpful, I think it's intended for use with sendfile()
Mark
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(no subject)
from:
krow
date: Feb. 27th, 2008 08:48 pm (UTC)
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