Re: [Xen-devel] [PATCH v4 09/10] xen/blkfront: make persistent grants per-queue

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Mon, Nov 02, 2015 at 12:21:45PM +0800, Bob Liu wrote:
> Make persistent grants per-queue/ring instead of per-device, so that we can
> drop the 'dev_lock' and get better scalability.

And what is the performance value for this? How much better
scalability do you get with this?
.. snip..
> @@ -1010,6 +1002,23 @@ static void blkif_free_ring(struct blkfront_ring_info 
> *rinfo)
>               }
>       }
>  
> +     /* Remove all persistent grants */

Missing full stop.
> +     if (!list_empty(&rinfo->grants)) {
> +             list_for_each_entry_safe(persistent_gnt, n,
> +                                      &rinfo->grants, node) {
> +                     list_del(&persistent_gnt->node);
> +                     if (persistent_gnt->gref != GRANT_INVALID_REF) {
> +                             gnttab_end_foreign_access(persistent_gnt->gref,
> +                                                       0, 0UL);
> +                             rinfo->persistent_gnts_c--;
> +                     }
> +                     if (info->feature_persistent)
> +                             __free_page(pfn_to_page(persistent_gnt->pfn));
> +                     kfree(persistent_gnt);
> +             }
> +     }
> +     BUG_ON(rinfo->persistent_gnts_c != 0);
> +

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