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Re: [Qemu-devel] [Xen-devel] [PATCH] qemu/xendisk: set maximum number of
From: |
Jan Beulich |
Subject: |
Re: [Qemu-devel] [Xen-devel] [PATCH] qemu/xendisk: set maximum number of grants to be used |
Date: |
Fri, 11 May 2012 15:19:20 +0100 |
>>> On 11.05.12 at 09:19, "Jan Beulich" <address@hidden> wrote:
> Legacy (non-pvops) gntdev drivers may require this to be done when the
> number of grants intended to be used simultaneously exceeds a certain
> driver specific default limit.
>
> Signed-off-by: Jan Beulich <address@hidden>
>
> --- a/hw/xen_disk.c
> +++ b/hw/xen_disk.c
> @@ -536,6 +536,10 @@ static void blk_alloc(struct XenDevice *
> if (xen_mode != XEN_EMULATE) {
> batch_maps = 1;
> }
> + if (xc_gnttab_set_max_grants(xendev->gnttabdev,
> + max_requests * BLKIF_MAX_SEGMENTS_PER_REQUEST + 1) < 0)
In more extensive testing it appears that very rarely this value is still
too low:
xen be: qdisk-768: can't map 11 grant refs (Cannot allocate memory, 342 maps)
342 + 11 = 353 > 352 = 32 * 11
Could someone help out here? I first thought this might be due to
use_aio being non-zero, but ioreq_start() doesn't permit more than
max_requests struct ioreqs-s to be around.
Additionally, shouldn't the driver be smarter and gracefully handle
grant mapping failures (as the per-domain map track table in the
hypervisor is a finite resource)?
Jan
> + xen_be_printf(xendev, 0, "xc_gnttab_set_max_grants failed: %s\n",
> + strerror(errno));
> }
>
> static int blk_init(struct XenDevice *xendev)