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

[FUJITA Tomonori]

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?

The Linux kernel AIO works only with Direct I/O (that is, we can't use
page cache with AIO). It's a huge problem for us so we don't use AIO
now.


> Is there a minimal linux kernel that supports this kind of AIO calls?
> Minimal RedHat distro?

I guess that all the distributions supports the kernel AIO. There is
no kernel option to disable it now.