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

From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
To: Bob Liu <bob.liu@oracle.com>
Cc: xen-devel@lists.xen.org, linux-kernel@vger.kernel.org,
	roger.pau@citrix.com, felipe.franciosi@citrix.com, axboe@fb.com,
	avanzini.arianna@gmail.com, rafal.mielniczuk@citrix.com,
	jonathan.davies@citrix.com, david.vrabel@citrix.com
Subject: Re: [PATCH v4 09/10] xen/blkfront: make persistent grants per-queue
Date: Wed, 4 Nov 2015 21:39:30 -0500	[thread overview]
Message-ID: <20151105023930.GC3949@x230.dumpdata.com> (raw)
In-Reply-To: <1446438106-20171-10-git-send-email-bob.liu@oracle.com>

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);
> +