Re: [PATCH 10/10] engines/libblkio: Share a single blkio instance among threads in same process

[Vincent Fu <vincentfu@gmail.com>]

On 11/21/22 13:29, Alberto Faria wrote:
> fio groups all subjobs that set option 'thread' into a single process.
> Have them all share a single `struct blkio` instance, with one `struct
> blkioq` per thread/subjob. This allows benchmarking multi-queue setups.
> 
> Note that `struct blkio` instances cannot be shared across different
> processes.
> 
> Signed-off-by: Alberto Faria <afaria@redhat.com>
> ---
>   HOWTO.rst                                 |   8 +-
>   engines/libblkio.c                        | 250 +++++++++++++++++++---
>   examples/libblkio-io_uring.fio            |  13 +-
>   examples/libblkio-virtio-blk-vfio-pci.fio |  13 +-
>   fio.1                                     |   7 +-
>   5 files changed, 257 insertions(+), 34 deletions(-)
> 
> diff --git a/HOWTO.rst b/HOWTO.rst
> index 763f4f51..4e69abfc 100644
> --- a/HOWTO.rst
> +++ b/HOWTO.rst
> @@ -2199,7 +2199,13 @@ I/O engine
>   			:option:`libblkio_driver`. If
>   			:option:`mem`/:option:`iomem` is not specified, memory
>   			allocation is delegated to libblkio (and so is
> -			guaranteed to work with the selected *driver*).
> +			guaranteed to work with the selected *driver*). One
> +			``struct blkio`` instance is used per process, so all
> +			jobs setting option :option:`thread` will share a single
> +			``struct blkio`` (with one queue per thread) and must
> +			specify compatible options. Note that some drivers don't
> +			allow several processes to access the same device or
> +			file simultaneously, but allow it for threads.
>   
>   I/O engine specific parameters
>   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> diff --git a/engines/libblkio.c b/engines/libblkio.c
> index a80be66f..987dea4f 100644
> --- a/engines/libblkio.c
> +++ b/engines/libblkio.c
> @@ -249,6 +249,105 @@ static int fio_blkio_set_props_from_str(struct blkio *b, const char *opt_name,
>   			blkio_get_error_msg()); \
>   	})
>   
> +static bool possibly_null_strs_equal(const char *a, const char *b)
> +{
> +	return (!a && !b) || (a && b && strcmp(a, b) == 0);
> +}
> +
> +/*
> + * Returns the total number of subjobs using option 'thread' in the entire
> + * workload that have the given value for the 'hipri' option.
> + */
> +static int total_threaded_subjobs(bool hipri)
> +{
> +	struct thread_data *td;
> +	unsigned int i;
> +	int count = 0;
> +
> +	for_each_td(td, i) {
> +		const struct fio_blkio_options *options = td->eo;
> +		if (td->o.use_thread && (bool)options->hipri == hipri)
> +			++count;
> +	}
> +
> +	return count;
> +}

The loop should skip jobs not using the libblkio ioengine because, for 
example, some ioengines don't have any ioengine options.