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[Xen-changelog] [linux-2.6.18-xen] improve floppy behavior

# HG changeset patch
# User Jan Beulich <jbeulich@xxxxxxxx>
# Date 1318491050 -7200
# Node ID f4a4962d40e425e13af4401e0f44141f82828064
# Parent  c7c14595c18b4ddc1a16e7b64352ba8ac21fbecf
improve floppy behavior

Timing is significantly different from native both because Xen traps
I/O port accesses and since DMA use is not possible (without intrusive
changes). Due to the overhead of trapped port accesses, I/O is already
slow enough (and Xen doesn't run on very old hardware anyway), so the
situation can easily be improved by not enforcing REALLY_SLOW_IO.

This doesn't completely address the issue - Xen just cannot guarantee
scheduling of a particular vCPU with a maximum latency of about 80us
(needed for the default FIFO threshold value of 10). The only complete
solution would require making ISA DMA usable on Xen.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

diff -r c7c14595c18b -r f4a4962d40e4 drivers/block/floppy.c
--- a/drivers/block/floppy.c    Tue Oct 11 15:08:10 2011 +0200
+++ b/drivers/block/floppy.c    Thu Oct 13 09:30:50 2011 +0200
@@ -146,7 +146,9 @@
+#ifndef CONFIG_XEN
 #define DEBUGT 2
 #define DCL_DEBUG              /* debug disk change line */

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