Re: [Xen-devel] [PATCH, v3] qemu/xendisk: set maximum number of grants to be used

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Thu, 31 May 2012, Jan Beulich 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.
> 
> Change in v2: Double the number requested, as we need to account for
> the allocations needing to happen in contiguous chunks. The worst case
> number would be max_req * max_seg + (max_req - 1) * (max_seg - 1) + 1,
> but in order to keep things simple just use 2 * max_req * max_seg.
> 
> Change in v3: introduce MAX_GRANTS(), and add a comment explaining its
> definition.
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

I think it is OK, I'll submit it as a bug fix for QEMU 1.1.

It should be applied to qemu-xen-traditional too.


> --- a/hw/xen_disk.c
> +++ b/hw/xen_disk.c
> @@ -537,6 +537,15 @@ static void blk_bh(void *opaque)
>      blk_handle_requests(blkdev);
>  }
>  
> +/*
> + * We need to account for the grant allocations requiring contiguous
> + * chunks; the worst case number would be
> + *     max_req * max_seg + (max_req - 1) * (max_seg - 1) + 1,
> + * but in order to keep things simple just use
> + *     2 * max_req * max_seg.
> + */
> +#define MAX_GRANTS(max_req, max_seg) (2 * (max_req) * (max_seg))
> +
>  static void blk_alloc(struct XenDevice *xendev)
>  {
>      struct XenBlkDev *blkdev = container_of(xendev, struct XenBlkDev, 
> xendev);
> @@ -548,6 +557,11 @@ static void blk_alloc(struct XenDevice *
>      if (xen_mode != XEN_EMULATE) {
>          batch_maps = 1;
>      }
> +    if (xc_gnttab_set_max_grants(xendev->gnttabdev,
> +            MAX_GRANTS(max_requests, BLKIF_MAX_SEGMENTS_PER_REQUEST)) < 0) {
> +        xen_be_printf(xendev, 0, "xc_gnttab_set_max_grants failed: %s\n",
> +                      strerror(errno));
> +    }
>  }
>  
>  static int blk_init(struct XenDevice *xendev)
> 
> 
> 
> 

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