[Qemu-devel] Re: memory usage and ioports

2007-11-19 Thread Samuel Thibault 
Samuel Thibault, le Mon 19 Nov 2007 15:20:16 +, a écrit :
 Qemu currently uses 6 65k tables of pointers for handling ioports, which
 makes 3MB on 64bit machines. There's a comment that says XXX: use a two
 level table to limit memory usage. But wouldn't it be more simple and
 effective to just allocate them through mmap() and when a NULL pointer
 is read, call the default handlers?

For the ioport_opaque array (500KB on 64bit), it's much simpler, as the
attached patch suggests.

Samuel
diff -r 6a6eace79e93 tools/ioemu/vl.c
--- qemu/vl.c   Mon Nov 19 15:04:05 2007 +
+++ qemu/vl.c   Mon Nov 19 15:31:35 2007 +
@@ -139,7 +139,7 @@
 
 const char *bios_dir = CONFIG_QEMU_SHAREDIR;
 char phys_ram_file[1024];
-void *ioport_opaque[MAX_IOPORTS];
+void **ioport_opaque;
 IOPortReadFunc *ioport_read_table[3][MAX_IOPORTS];
 IOPortWriteFunc *ioport_write_table[3][MAX_IOPORTS];
 /* Note: bs_table[MAX_DISKS] is a dummy block driver if none available
@@ -265,6 +265,7 @@ void init_ioports(void)
 {
 int i;
 
+ioport_opaque = malloc(MAX_IOPORTS * sizeof(*ioport_opaque));
 for(i = 0; i  MAX_IOPORTS; i++) {
 ioport_read_table[0][i] = default_ioport_readb;
 ioport_write_table[0][i] = default_ioport_writeb;

Re: [Qemu-devel] Re: memory usage and ioports

2007-11-19 Thread Paul Brook 
On Monday 19 November 2007, Samuel Thibault wrote:
 Samuel Thibault, le Mon 19 Nov 2007 15:20:16 +, a écrit :
  Qemu currently uses 6 65k tables of pointers for handling ioports, which
  makes 3MB on 64bit machines. There's a comment that says XXX: use a two
  level table to limit memory usage. But wouldn't it be more simple and
  effective to just allocate them through mmap() and when a NULL pointer
  is read, call the default handlers?

 For the ioport_opaque array (500KB on 64bit), it's much simpler, as the
 attached patch suggests.

AFAICS This makes absolutely no difference to memory usage.

Paul

Re: [Qemu-devel] Re: memory usage and ioports

2007-11-19 Thread Samuel Thibault 
Paul Brook, le Mon 19 Nov 2007 16:17:26 +, a écrit :
 On Monday 19 November 2007, Samuel Thibault wrote:
  Samuel Thibault, le Mon 19 Nov 2007 15:20:16 +, a écrit :
   Qemu currently uses 6 65k tables of pointers for handling ioports, which
   makes 3MB on 64bit machines. There's a comment that says XXX: use a two
   level table to limit memory usage. But wouldn't it be more simple and
   effective to just allocate them through mmap() and when a NULL pointer
   is read, call the default handlers?
 
  For the ioport_opaque array (500KB on 64bit), it's much simpler, as the
  attached patch suggests.
 
 AFAICS This makes absolutely no difference to memory usage.

Ah, sorry, in a unix environment it doesn't indeed.  In an embedded
environment or so which has to provide a fully allocated bss because it
doesn't have cow support early enough, that makes a difference.

Samuel