[Qemu-devel] [PATCH] -win2k-hack performance+DMA support

["Leonardo E. Reiter" <lreiter@win4lin.com>]

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Attached is a patch which greatly speeds up disk writes when using 
-win2k-hack to install Windows 2000.  It only delays every 16th 
interrupt, which after rigorous testing is still enough to overcome the 
"Windows 2000 disk full" bug.  If you are really adventurous you can try 
it every 32nd time, but for me that caused problems during some 
installations, so I thought it was too aggressive.

This patch also adds -win2k-hack functionality to DMA writes, since DMA 
now works in the latest CVS QEMU.

Enjoy,

Leo Reiter

-- 
Leonardo E. Reiter
Vice President of Product Development, CTO

Win4Lin, Inc.
Virtual Computing from Desktop to Data Center
Main: +1 512 339 7979
Fax: +1 512 532 6501
http://www.win4lin.com

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Index: hw/ide.c
===================================================================
RCS file: /cvsroot/qemu/qemu/hw/ide.c,v
retrieving revision 1.39
diff -a -u -r1.39 ide.c
--- hw/ide.c	1 Feb 2006 22:20:12 -0000	1.39
+++ hw/ide.c	2 Feb 2006 01:48:25 -0000
@@ -336,6 +336,7 @@
     uint8_t *data_end;
     uint8_t io_buffer[MAX_MULT_SECTORS*512 + 4];
     QEMUTimer *sector_write_timer; /* only used for win2k instal hack */
+    uint32_t irq_count; /* counts IRQs when using win2k install hack */
 } IDEState;
 
 #define BM_STATUS_DMAING 0x01
@@ -712,7 +713,7 @@
     ide_set_sector(s, sector_num + n);
     
 #ifdef TARGET_I386
-    if (win2k_install_hack) {
+    if (win2k_install_hack && ((++s->irq_count % 16) == 0)) {
         /* It seems there is a bug in the Windows 2000 installer HDD
            IDE driver which fills the disk with empty logs when the
            IDE write IRQ comes too early. This hack tries to correct
@@ -750,7 +751,19 @@
             if (n == 0) {
                 /* end of transfer */
                 s->status = READY_STAT | SEEK_STAT;
-                ide_set_irq(s);
+#ifdef TARGET_I386
+                if (win2k_install_hack && ((++s->irq_count % 16) == 0)) {
+                    /* It seems there is a bug in the Windows 2000 installer 
+                       HDD IDE driver which fills the disk with empty logs 
+                       when the IDE write IRQ comes too early. This hack tries 
+                       to correct that at the expense of slower write 
+                       performances. Use this option _only_ to install Windows 
+                       2000. You must disable it for normal use. */
+                    qemu_mod_timer(s->sector_write_timer, 
+                            qemu_get_clock(vm_clock) + (ticks_per_sec / 1000));
+                } else 
+#endif
+                    ide_set_irq(s);
                 return 0;
             }
             if (n > MAX_MULT_SECTORS)