On 12/5/08, Anthony Liguori <[EMAIL PROTECTED]> wrote:
> glibc implements posix-aio as a thread pool and imposes a number of
> limitations.
>
> 1) it limits one request per-file descriptor. we hack around this by
> dup()'ing
> file descriptors which is hideously ugly
>
> 2) it's impossible to add new interfaces and we need a vectored read/write
> operation to properly support a zero-copy API.
>
> What has been suggested to me by glibc folks, is to implement whatever new
> interfaces we want and then it can eventually be proposed for
> standardization.
> This requires that we implement our own posix-aio implementation though.
>
> This patch implements posix-aio using pthreads. It immediately eliminates
> the
> need for fd pooling.
>
> It performs at least as well as the current posix-aio code (in some
> circumstances, even better).
>
> My only concern here is non-Linux Unices like FreeBSD. They have kernel
> support
> for posix-aio. Since we cannot extend those interfaces though, I think that
> even on those platforms we should still use a thread pool.
>
> Signed-off-by: Anthony Liguori <[EMAIL PROTECTED]>
> @@ -895,6 +824,7 @@ BlockDriver bdrv_raw = {
> .bdrv_aio_cancel = raw_aio_cancel,
> .aiocb_size = sizeof(RawAIOCB),
> #endif
> +
> @@ -1252,6 +1178,7 @@ BlockDriver bdrv_host_device = {
> .bdrv_aio_cancel = raw_aio_cancel,
> .aiocb_size = sizeof(RawAIOCB),
> #endif
> +
Some cleanup needed here?
> +int _compat_aio_init(struct aioinit *aioinit)
> +static int _compat_aio_submit(struct aiocb *aiocb, int is_write)
> +int _compat_aio_read(struct aiocb *aiocb)
> +int _compat_aio_write(struct aiocb *aiocb)
> +ssize_t _compat_aio_return(struct aiocb *aiocb)
> +int _compat_aio_error(struct aiocb *aiocb)
> +int _compat_aio_cancel(int fd, struct aiocb *aiocb)
The names should not begin with an underscore.
> +struct aiocb
> +{
> + int aio_fildes;
> + void *aio_buf;
> + size_t aio_nbytes;
> + struct sigevent aio_sigevent;
> + off_t aio_offset;
> +
> + /* private */
> + TAILQ_ENTRY(aiocb) node;
> + int is_write;
> + ssize_t ret;
> + int active;
> +};
> +
> +struct aioinit
> +{
> + int aio_threads;
> + int aio_num;
> + int aio_idle_time;
> +};
These structs should probably be named qemu_aiocb and qemu_aioinit to
avoid conflict with system types.
I like to use unsigned types whenever possible, IIRC compilers may
generate better code with those.
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to [EMAIL PROTECTED]
More majordomo info at http://vger.kernel.org/majordomo-info.html
