Re: [Xen-devel] [PATCH] tools/libxc: Batch memory allocations for PV guests

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Wed, Jun 10, 2015 at 02:38:15PM +0100, Ross Lagerwall wrote:
> The current code for allocating memory for PV guests batches the
> hypercalls to allocate memory by allocating 1024*1024 extents of order 0
> at a time. To make this faster, first try allocating single extents of
> order 9 (2 MiB) before falling back to the order 0 allocating if the
> order 9 allocation fails.
> 
> On my test machine this reduced the time to start a 128 GiB PV guest by
> about 60 seconds.
> 
> Signed-off-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>

> ---
>  tools/libxc/xc_dom_x86.c | 22 ++++++++++++++++++++--
>  1 file changed, 20 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/libxc/xc_dom_x86.c b/tools/libxc/xc_dom_x86.c
> index 783f749..a674d39 100644
> --- a/tools/libxc/xc_dom_x86.c
> +++ b/tools/libxc/xc_dom_x86.c
> @@ -761,7 +761,7 @@ int arch_setup_meminit(struct xc_dom_image *dom)
>  {
>      int rc;
>      xen_pfn_t pfn, allocsz, mfn, total, pfn_base;
> -    int i, j;
> +    int i, j, k;
>  
>      rc = x86_compat(dom->xch, dom->guest_domid, dom->guest_type);
>      if ( rc )
> @@ -881,7 +881,25 @@ int arch_setup_meminit(struct xc_dom_image *dom)
>              for ( pfn = pfn_base; pfn < pfn_base+pages; pfn++ )
>                  dom->p2m_host[pfn] = pfn;
>  
> -            for ( j = 0; j < pages; j += allocsz )
> +            for ( j = 0; j < pages; )
> +            {
> +                if ( (pages - j) < SUPERPAGE_NR_PFNS )
> +                    break;
> +
> +                mfn = dom->p2m_host[pfn_base + j];
> +                rc = xc_domain_populate_physmap(dom->xch, dom->guest_domid, 
> 1,
> +                         SUPERPAGE_PFN_SHIFT, memflags, &mfn);
> +
> +                if ( rc != 1 )
> +                    break;
> +

If you want to optimise you might as well consider batching to reduce
the number of hypercall made. See dom->superpages path.

Wei.

> +                for ( k = 0; k < SUPERPAGE_NR_PFNS; k++, j++ )
> +                    dom->p2m_host[pfn_base + j] = mfn + k;
> +            }
> +
> +            rc = 0;
> +            for ( ; j < pages; j += allocsz )
>              {


>                  allocsz = pages - j;
>                  if ( allocsz > 1024*1024 )
> -- 
> 2.1.0

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