Re: [PATCH] libosd: osd_req_read_sg, optimize the single entry case

[Boaz Harrosh <bharrosh@panasas.com>]

On 01/23/2011 05:53 PM, Boaz Harrosh wrote:
> 
> Since sg-read is a bidi operation, it is a gain to convert
> a single sg entry into a regular read. Better do this in the
> generic layer then force each caller to do so.
> 
> Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
> ---
>  drivers/scsi/osd/osd_initiator.c |   20 ++++++++++++++++----
>  1 files changed, 16 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/scsi/osd/osd_initiator.c b/drivers/scsi/osd/osd_initiator.c
> index 0433ea6..19ddf65 100644
> --- a/drivers/scsi/osd/osd_initiator.c
> +++ b/drivers/scsi/osd/osd_initiator.c
> @@ -1005,11 +1005,23 @@ int osd_req_read_sg(struct osd_request *or,
>  	const struct osd_sg_entry *sglist, unsigned numentries)
>  {
>  	u64 len;
> -	int ret = _add_sg_continuation_descriptor(or, sglist, numentries, &len);
> +	u64 off;
> +	int ret;
>  
> -	if (ret)
> -		return ret;
> -	osd_req_read(or, obj, 0, bio, len);
> +	if (numentries > 1) {
> +		off = 0;
> +		ret = _add_sg_continuation_descriptor(or, sglist, numentries,
> +						      &len);
> +		if (ret)
> +			return ret;
> +	} else {
> +		/* Optimize the case of single segment, read_sg is a
> +		 * bidi operation.
> +		 */
> +		len = sglist->len;
> +		off = sglist->offset;
> +	}
> +	osd_req_read(or, obj, off, bio, len);
>  
>  	return 0;
>  }

James please include this patch into scsi-misc for the next merge window.

Thanks
Boaz