Re: [Qemu-devel] [PATCH] exec: optimize phys_page_set_level

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Thu, May 21, 2015 at 03:19:58PM +0200, Paolo Bonzini wrote:
> phys_page_set_level is writing zeroes to a struct that has just been
> filled in by phys_map_node_alloc.  Instead, tell phys_map_node_alloc
> whether to fill in the page "as a leaf" or "as a non-leaf".
> 
> memcpy is faster than struct assignment, which copies each bitfield
> individually.  Arguably a compiler bug, but memcpy is super-special
> cased anyway so what could go wrong?
> 
> This cuts the cost of phys_page_set_level from 25% to 5% when
> booting qboot.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  exec.c | 24 ++++++++++--------------
>  1 file changed, 10 insertions(+), 14 deletions(-)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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