On 03/16/2010 07:45 AM, Avi Kivity wrote:
On 03/16/2010 12:53 PM, Yoshiaki Tamura wrote:
Modifies wrapper functions for byte-based phys_ram_dirty bitmap to
bit-based phys_ram_dirty bitmap, and adds more wrapper functions to
prevent
direct access to the phys_ram_dirty bitmap.
+
+static inline int cpu_physical_memory_get_dirty_flags(ram_addr_t addr)
+{
+ unsigned long mask;
+ int index = (addr>> TARGET_PAGE_BITS) / HOST_LONG_BITS;
+ int offset = (addr>> TARGET_PAGE_BITS)& (HOST_LONG_BITS - 1);
+ int ret = 0;
+
+ mask = 1UL<< offset;
+ if (phys_ram_vga_dirty[index]& mask)
+ ret |= VGA_DIRTY_FLAG;
+ if (phys_ram_code_dirty[index]& mask)
+ ret |= CODE_DIRTY_FLAG;
+ if (phys_ram_migration_dirty[index]& mask)
+ ret |= MIGRATION_DIRTY_FLAG;
+
+ return ret;
}
static inline int cpu_physical_memory_get_dirty(ram_addr_t addr,
int dirty_flags)
{
- return phys_ram_dirty[addr>> TARGET_PAGE_BITS]& dirty_flags;
+ return cpu_physical_memory_get_dirty_flags(addr)& dirty_flags;
}
This turns one cacheline access into three. If the dirty bitmaps were
in an array, you could do
return dirty_bitmaps[dirty_index][addr >> (TARGET_PAGE_BITS +
BITS_IN_LONG)] & mask;
with one cacheline access.
As far as I can tell, we only ever call with a single flag so your
suggestion makes sense.
I'd suggest introducing these functions before splitting the bitmap up.
It makes review a bit easier.
static inline void cpu_physical_memory_set_dirty(ram_addr_t addr)
{
- phys_ram_dirty[addr>> TARGET_PAGE_BITS] = 0xff;
+ unsigned long mask;
+ int index = (addr>> TARGET_PAGE_BITS) / HOST_LONG_BITS;
+ int offset = (addr>> TARGET_PAGE_BITS)& (HOST_LONG_BITS - 1);
+
+ mask = 1UL<< offset;
+ phys_ram_vga_dirty[index] |= mask;
+ phys_ram_code_dirty[index] |= mask;
+ phys_ram_migration_dirty[index] |= mask;
+}
This is also three cacheline accesses. I think we should have a
master bitmap which is updated by set_dirty(), and which is or'ed into
the other bitmaps when they are accessed. At least the vga and
migration bitmaps are only read periodically, not randomly, so this
would be very fast. In a way, this is similar to how the qemu bitmap
is updated from the kvm bitmap today.
I am not sure about the code bitmap though.
I think your suggestion makes sense and would also work for the code bitmap.
Regards,
Anthony Liguori
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