Patchwork [4/5] exec.c: refactor cpu_physical_memory_map

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Submitter Stefano Stabellini
Date May 18, 2011, 5:52 p.m.
Message ID <1305741151-4793-4-git-send-email-stefano.stabellini@eu.citrix.com>
Download mbox | patch
Permalink /patch/96209/
State New
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Comments

Stefano Stabellini - May 18, 2011, 5:52 p.m.
From: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

Introduce qemu_ram_ptr_length that takes an address and a size as
parameters rather than just an address.

Refactor cpu_physical_memory_map so that we call qemu_ram_ptr_length only
once rather than calling qemu_get_ram_ptr one time per page.
This is not only more efficient but also tries to simplify the logic of
the function.
Currently we are relying on the fact that all the pages are mapped
contiguously in qemu's address space: we have a check to make sure that
the virtual address returned by qemu_get_ram_ptr from the second call on
is consecutive. Now we are making this more explicit replacing all the
calls to qemu_get_ram_ptr with a single call to qemu_ram_ptr_length
passing a size argument.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
CC: agraf@suse.de
CC: anthony@codemonkey.ws
---
 cpu-common.h |    1 +
 exec.c       |   51 ++++++++++++++++++++++++++++++++++-----------------
 2 files changed, 35 insertions(+), 17 deletions(-)
Paolo Bonzini - May 18, 2011, 9:56 p.m.
On 05/18/2011 07:52 PM, stefano.stabellini@eu.citrix.com wrote:
> From: Stefano Stabellini<stefano.stabellini@eu.citrix.com>
>
> Introduce qemu_ram_ptr_length that takes an address and a size as
> parameters rather than just an address.
>
> Refactor cpu_physical_memory_map so that we call qemu_ram_ptr_length only
> once rather than calling qemu_get_ram_ptr one time per page.
> This is not only more efficient but also tries to simplify the logic of
> the function.
> Currently we are relying on the fact that all the pages are mapped
> contiguously in qemu's address space: we have a check to make sure that
> the virtual address returned by qemu_get_ram_ptr from the second call on
> is consecutive. Now we are making this more explicit replacing all the
> calls to qemu_get_ram_ptr with a single call to qemu_ram_ptr_length
> passing a size argument.

Would the interface at 
http://permalink.gmane.org/gmane.comp.emulators.qemu/101475 work for you 
alternatively?

Paolo
Stefano Stabellini - May 19, 2011, 5:21 p.m.
On Wed, 18 May 2011, Paolo Bonzini wrote:
> On 05/18/2011 07:52 PM, stefano.stabellini@eu.citrix.com wrote:
> > From: Stefano Stabellini<stefano.stabellini@eu.citrix.com>
> >
> > Introduce qemu_ram_ptr_length that takes an address and a size as
> > parameters rather than just an address.
> >
> > Refactor cpu_physical_memory_map so that we call qemu_ram_ptr_length only
> > once rather than calling qemu_get_ram_ptr one time per page.
> > This is not only more efficient but also tries to simplify the logic of
> > the function.
> > Currently we are relying on the fact that all the pages are mapped
> > contiguously in qemu's address space: we have a check to make sure that
> > the virtual address returned by qemu_get_ram_ptr from the second call on
> > is consecutive. Now we are making this more explicit replacing all the
> > calls to qemu_get_ram_ptr with a single call to qemu_ram_ptr_length
> > passing a size argument.
> 
> Would the interface at 
> http://permalink.gmane.org/gmane.comp.emulators.qemu/101475 work for you 
> alternatively?

Unfortunately that interface doesn't solve the problem I am trying to
address:

cpu_physical_memory_map_fast calls cpu_physical_memory_map_internal that
still calls qemu_get_ram_ptr in a loop.

Patch

diff --git a/cpu-common.h b/cpu-common.h
index 151c32c..085aacb 100644
--- a/cpu-common.h
+++ b/cpu-common.h
@@ -64,6 +64,7 @@  void qemu_ram_free(ram_addr_t addr);
 void qemu_ram_remap(ram_addr_t addr, ram_addr_t length);
 /* This should only be used for ram local to a device.  */
 void *qemu_get_ram_ptr(ram_addr_t addr);
+void *qemu_ram_ptr_length(target_phys_addr_t addr, target_phys_addr_t *size);
 /* Same but slower, to use for migration, where the order of
  * RAMBlocks must not change. */
 void *qemu_safe_ram_ptr(ram_addr_t addr);
diff --git a/exec.c b/exec.c
index 56bc636..ee9316e 100644
--- a/exec.c
+++ b/exec.c
@@ -3110,6 +3110,31 @@  void *qemu_safe_ram_ptr(ram_addr_t addr)
     return NULL;
 }
 
+/* Return a host pointer to guest's ram. Similar to qemu_get_ram_ptr
+ * but takes a size argument */
+void *qemu_ram_ptr_length(target_phys_addr_t addr, target_phys_addr_t *size)
+{
+    if (xen_mapcache_enabled())
+        return qemu_map_cache(addr, *size, 1);
+    else {
+        RAMBlock *block;
+
+        QLIST_FOREACH(block, &ram_list.blocks, next) {
+            if (addr - block->offset < block->length) {
+                if (addr - block->offset + *size > block->length)
+                    *size = block->length - addr + block->offset;
+                return block->host + (addr - block->offset);
+            }
+        }
+
+        fprintf(stderr, "Bad ram offset %" PRIx64 "\n", (uint64_t)addr);
+        abort();
+
+        *size = 0;
+        return NULL;
+    }
+}
+
 void qemu_put_ram_ptr(void *addr)
 {
     trace_qemu_put_ram_ptr(addr);
@@ -3971,14 +3996,12 @@  void *cpu_physical_memory_map(target_phys_addr_t addr,
                               int is_write)
 {
     target_phys_addr_t len = *plen;
-    target_phys_addr_t done = 0;
+    target_phys_addr_t todo = 0;
     int l;
-    uint8_t *ret = NULL;
-    uint8_t *ptr;
     target_phys_addr_t page;
     unsigned long pd;
     PhysPageDesc *p;
-    unsigned long addr1;
+    target_phys_addr_t addr1 = addr;
 
     while (len > 0) {
         page = addr & TARGET_PAGE_MASK;
@@ -3993,7 +4016,7 @@  void *cpu_physical_memory_map(target_phys_addr_t addr,
         }
 
         if ((pd & ~TARGET_PAGE_MASK) != IO_MEM_RAM) {
-            if (done || bounce.buffer) {
+            if (todo || bounce.buffer) {
                 break;
             }
             bounce.buffer = qemu_memalign(TARGET_PAGE_SIZE, TARGET_PAGE_SIZE);
@@ -4002,23 +4025,17 @@  void *cpu_physical_memory_map(target_phys_addr_t addr,
             if (!is_write) {
                 cpu_physical_memory_read(addr, bounce.buffer, l);
             }
-            ptr = bounce.buffer;
-        } else {
-            addr1 = (pd & TARGET_PAGE_MASK) + (addr & ~TARGET_PAGE_MASK);
-            ptr = qemu_get_ram_ptr(addr1);
-        }
-        if (!done) {
-            ret = ptr;
-        } else if (ret + done != ptr) {
-            break;
+
+            *plen = l;
+            return bounce.buffer;
         }
 
         len -= l;
         addr += l;
-        done += l;
+        todo += l;
     }
-    *plen = done;
-    return ret;
+    *plen = todo;
+    return qemu_ram_ptr_length(addr1, plen);
 }
 
 /* Unmaps a memory region previously mapped by cpu_physical_memory_map().