[Spice-devel] [PATCH 10/12] qxl-wddm-dod: Optimize allocation of memory chunks

[Frediano Ziglio]

> On Tue, Mar 28, 2017 at 4:23 PM, Frediano Ziglio < fziglio at redhat.com >
> wrote:

> > >
> 
> > > Increased size of allocation to reduce number of allocation per
> 
> > > bitmap. Before change the procedure ignored 'alloc_size' parameter
> 
> > > and always allocated memory chunk according to 'size' parameter.
> 
> > > As a result, first chunk could be up to 64K and all following are
> 
> > > limited by line size. For example, for bitmap 1280x1024 there was
> 
> > > more than 1008 chunks allocated, for bitmap 128x1024 - 897 chunks.
> 
> > > We change the procedure to use chunk size up to 64K (similar to first
> 
> > > chunk). This reduces in described examples number of allocation from
> 
> > > 1008 to 64 and 897 to 8 respectively.
> 
> > >
> 
> > > Signed-off-by: Yuri Benditovich < yuri.benditovich at daynix.com >
> 
> > > ---
> 
> > > qxldod/QxlDod.cpp | 2 +-
> 
> > > 1 file changed, 1 insertion(+), 1 deletion(-)
> 
> > >
> 
> > > diff --git a/qxldod/QxlDod.cpp b/qxldod/QxlDod.cpp
> 
> > > index 56a4cf2..94426dd 100755
> 
> > > --- a/qxldod/QxlDod.cpp
> 
> > > +++ b/qxldod/QxlDod.cpp
> 
> > > @@ -4586,7 +4586,7 @@ BOOLEAN QxlDevice::PutBytesAlign(QXLDataChunk
> 
> > > **chunk_ptr, UINT8 **now_ptr,
> 
> > > UINT8 *now = *now_ptr;
> 
> > > UINT8 *end = *end_ptr;
> 
> > > size_t maxAllocSize = BITS_BUF_MAX - BITS_BUF_MAX % size;
> 
> > > - alloc_size = MIN(size, maxAllocSize);
> 
> > > + alloc_size = MIN(alloc_size, maxAllocSize);
> 
> > > DbgPrint(TRACE_LEVEL_VERBOSE, ("---> %s\n", __FUNCTION__));
> 
> > >
> 
> > > while (size) {
> 

> > As far as I can see this fix a regression introduced in 9/12 so
> 
> > should be squashed together with 9/12.
> 

> There was no regression in 9/12, see commit description
> This patch forces the driver to make bigger allocations and in result we will
> have smaller amount of allocations per operation.

Yes, you are right, there is this computation 

aligned_size = (int)MIN(alloc_size + alignment - 1, BITS_BUF_MAX); 
aligned_size -= aligned_size % alignment; 

but then the value is discarded and size is used instead. 

> > On the same subject. Why we need to split the allocations?
> 
> > Can't we try to allocate the whole image in one chunk and
> 
> > only if fails fall back to multiple chunks ?
> 

> No, we can't do that, as maximal size of allocation from device memory in
> driver's code was always limited by ~64K.
> So allocation were always splitted, see numbers in commit description.
> I suppose there is some reason for that.

Honestly knowing the server part I don't see any reasons. Maybe an history one... 

Frediano 
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