[Stgt-devel] [PATCH] Make changes so that VTL stuff works properly ...

[FUJITA Tomonori]

On Fri, 8 Aug 2008 08:04:11 +1000
"ronnie sahlberg" <ronniesahlberg at gmail.com> wrote:

> On Fri, Aug 8, 2008 at 4:14 AM, FUJITA Tomonori
> <fujita.tomonori at lab.ntt.co.jp> wrote:
> > On Wed, 6 Aug 2008 18:06:26 +0300
> > "Alexander Nezhinsky" <nezhinsky at gmail.com> wrote:
> >
> >> On Wed, Jul 30, 2008 at 10:04 AM, FUJITA Tomonori
> >> <fujita.tomonori at lab.ntt.co.jp> wrote:
> >>
> >> > the future... We have it just because Linux AIO is not good enough
> >> > now.
> >>
> >> Can you explain a bit what's wrong with the current Linux AIO implementation.
> >> Why bs_aio.c is implemented using syscall(__NR_io_*)?
> >> What is wrong with the aio_read/aio_write and friends?
> >
> >
> > I think that that's Posix AIO, which glibc implemented. It's slower
> > than the kernel AIO support. A big problem about it for us is event
> > notification. We can't get AIO completion events via a file descriptor
> > (so that we can't use poll/epoll with it). How can we wait for both
> > network events and AIO events at the same time?
> 
> What about setting up a pipe, forking, doing the the i/o in the child
> and then writing a byte of data to the pipe when the command completed.
> The parent can then "wait for the 'AIO' to complete by waiting on a
> file descriptor" like normal.

We did the similar thing. We don't fork every time we get a
request. Instead we keep several processes to perform requests.

But using a pipe is not the fastest way. I really like to move to the
real AIO solution.