Re: [Qemu-devel] [PATCH v2 0/3] memory: an optimization

[Fam Zheng <famz@redhat.com>]

On Mon, 02/22 11:22, Paolo Bonzini wrote:
> 
> 
> On 22/02/2016 09:34, Gonglei wrote:
> > Perf top tells me qemu_get_ram_ptr consume some cpu cycles.
> > 
> > Before this optimization:
> >   1.26%  qemu-kvm                  [.] qemu_get_ram_ptr
> >   0.89%  qemu-kvm                  [.] qemu_get_ram_block
> > 
> > Applied the patch set:
> >  0.87%  qemu-kvm                 [.] qemu_get_ram_ptr
> > 
> > And Paolo suggested that we can get rid of qemu_get_ram_ptr
> > by storing the RAMBlock pointer into the memory region,
> > instead of the ram_addr_t value. And after appling this change,
> > I got much better performance indeed.
> > 
> > BTW, PATCH 3 is an occasional find.
> > 
> > v2:
> >  - using 'struct RAMBlock *' instead of 'void *' in patch 1 [Fam]
> >  - drop superfluous comments in patch 1 [Fam]
> > 
> > Gonglei (3):
> >   exec: store RAMBlock pointer into memory region
> >   memory: optimize qemu_get_ram_ptr and qemu_ram_ptr_length
> >   memory: Remove the superfluous code
> > 
> >  exec.c                | 48 ++++++++++++++++++++++++++++++------------------
> >  include/exec/memory.h |  8 ++++----
> >  memory.c              |  3 ++-
> >  3 files changed, 36 insertions(+), 23 deletions(-)
> > 
> 
> Thanks Lei and Fam, patches queued.

Thanks!

Actually I'd like to clean this up a bit more: moving assigning to
mr->ram_block from exec.c to memory.c, and drop mr->ram_addr.

I've already done these on top of master last Friday before v1 of this was
posted (oops! :), but I can rebase on top of these patches.

And upon that, I think we can replicate the ram_list.mru_block trick as
AddressSpaceDispatch.mru_section, to further reduce the calls to
qemu_get_ram_ptr.

Paolo, is there a git branch I can base off?

Fam