regarding generic AIO, async syscalls precedent + some benchmarks by lighttpd

regarding generic AIO, async syscalls precedent + some benchmarks by lighttpd

[bert hubert]

>From two comments posted to my "blog"
http://blog.netherlabs.nl/articles/2007/02/04/a-synchronous-programming

Excerpted from the diary of Dragonfly BSD,
http://www.dragonflybsd.org/status/diary.shtml 

 Remove the asynchronous syscall interface. It was an idea before its time.
 However, keep the formalization of the syscall arguments structures.

The original async syscall interface was committed in
http://leaf.dragonflybsd.org/mailarchive/commits/2004-08/msg00067.html

Comment by Jan Kneschke, lighttpd developer, noting the lack of and need for
aio_stat():

 Reading this article feels like reading the code I wrote in the last days
 for lighttpd. Even if the network-io was async since the start
 (non-blocking), the file-io wasn't. Worst of all was the stat() syscall
 which doesn't have a async interface even in POSIX AIO. So it had to be
 implemented with threads on our own. At http://www.lighttpd.net/benchmark/
 you can see the impact of async vs. blocking syscalls.

Perhaps relevant.

-- 
http://www.PowerDNS.com      Open source, database driven DNS Software 
http://netherlabs.nl              Open and Closed source services

Re: regarding generic AIO, async syscalls precedent + some benchmarks by lighttpd

[Davide Libenzi]

On Sun, 4 Feb 2007, bert hubert wrote:

> >From two comments posted to my "blog"
> http://blog.netherlabs.nl/articles/2007/02/04/a-synchronous-programming
> 
> Excerpted from the diary of Dragonfly BSD,
> http://www.dragonflybsd.org/status/diary.shtml 
> 
>  Remove the asynchronous syscall interface. It was an idea before its time.
>  However, keep the formalization of the syscall arguments structures.
> 
> The original async syscall interface was committed in
> http://leaf.dragonflybsd.org/mailarchive/commits/2004-08/msg00067.html
> 
> Comment by Jan Kneschke, lighttpd developer, noting the lack of and need for
> aio_stat():
> 
>  Reading this article feels like reading the code I wrote in the last days
>  for lighttpd. Even if the network-io was async since the start
>  (non-blocking), the file-io wasn't. Worst of all was the stat() syscall
>  which doesn't have a async interface even in POSIX AIO. So it had to be
>  implemented with threads on our own. At http://www.lighttpd.net/benchmark/
>  you can see the impact of async vs. blocking syscalls.
> 
> Perhaps relevant.

Yes, that is some very interesting data IMO. I did not bench the GUASI 
(userspace async thread library) against AIO, but those numbers show that a 
*userspace* async syscall wrapper interface performs in the ballpark of AIO.
This leads to some hope about the ability to effectively deploy the kernel 
generic async AIO (being it fibril or kthreads based) as low-impact async 
provider for basically anything.



- Davide

Re: regarding generic AIO, async syscalls precedent + some benchmarks by lighttpd

[Christopher Smith]

Davide Libenzi wrote:
> Yes, that is some very interesting data IMO. I did not bench the GUASI 
> (userspace async thread library) against AIO, but those numbers show that a 
> *userspace* async syscall wrapper interface performs in the ballpark of AIO.
> This leads to some hope about the ability to effectively deploy the kernel 
> generic async AIO (being it fibril or kthreads based) as low-impact async 
> provider for basically anything.
>   

SGI's kaio patch to linux kind of went that route (using kthreads) for 
non-SCSI async IO. It wasn't a bad way to go, but at least for 
disk-based access they achieved much better results when they could go 
right to the hardware.

--Chris