Re: [Qemu-devel] [PATCH 07/15] memory: avoid ref/unref in memory_region_find

2015-01-26 Thread Paolo Bonzini 


On 26/01/2015 07:24, Fam Zheng wrote:
  Do the entire lookup under RCU, which avoids atomic operations.
 address_space_get_flatview() already is RCU protected, I don't see why this
 patch is necessary. Could you explain?

It's just an optimization; flatview_ref/flatview_unref do
atomic_inc/atomic_dec and this patch avoids that.

Paolo

Re: [Qemu-devel] [PATCH 07/15] memory: avoid ref/unref in memory_region_find

2015-01-25 Thread Fam Zheng 
On Thu, 01/22 15:47, Paolo Bonzini wrote:
 Do the entire lookup under RCU, which avoids atomic operations.

address_space_get_flatview() already is RCU protected, I don't see why this
patch is necessary. Could you explain?

And there is one question below:

 
 Signed-off-by: Paolo Bonzini pbonz...@redhat.com
 ---
  memory.c | 5 +++--
  1 file changed, 3 insertions(+), 2 deletions(-)
 
 diff --git a/memory.c b/memory.c
 index a844ced..577e87c 100644
 --- a/memory.c
 +++ b/memory.c
 @@ -1828,7 +1828,8 @@ MemoryRegionSection memory_region_find(MemoryRegion *mr,
  }
  range = addrrange_make(int128_make64(addr), int128_make64(size));
  
 -view = address_space_get_flatview(as);
 +rcu_read_lock();
 +view = atomic_rcu_read(as-current_map);
  fr = flatview_lookup(view, range);
  if (!fr) {
  flatview_unref(view);

Following lines are:

   return ret;
   }

Which requires a rcu_read_unlock.

Fam

 @@ -1850,7 +1851,7 @@ MemoryRegionSection memory_region_find(MemoryRegion *mr,
  ret.readonly = fr-readonly;
  memory_region_ref(ret.mr);
  
 -flatview_unref(view);
 +rcu_read_unlock();
  return ret;
  }
  
 -- 
 1.8.3.1

[Qemu-devel] [PATCH 07/15] memory: avoid ref/unref in memory_region_find

2015-01-22 Thread Paolo Bonzini 
Do the entire lookup under RCU, which avoids atomic operations.

Signed-off-by: Paolo Bonzini pbonz...@redhat.com
---
 memory.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/memory.c b/memory.c
index a844ced..577e87c 100644
--- a/memory.c
+++ b/memory.c
@@ -1828,7 +1828,8 @@ MemoryRegionSection memory_region_find(MemoryRegion *mr,
 }
 range = addrrange_make(int128_make64(addr), int128_make64(size));
 
-view = address_space_get_flatview(as);
+rcu_read_lock();
+view = atomic_rcu_read(as-current_map);
 fr = flatview_lookup(view, range);
 if (!fr) {
 flatview_unref(view);
@@ -1850,7 +1851,7 @@ MemoryRegionSection memory_region_find(MemoryRegion *mr,
 ret.readonly = fr-readonly;
 memory_region_ref(ret.mr);
 
-flatview_unref(view);
+rcu_read_unlock();
 return ret;
 }
 
-- 
1.8.3.1