Increasing swiotlb default

Increasing swiotlb default

[Andi Kleen]

Hallo,

I discovered that swiotlb defaults to using only 2MB of RAM by default. That's IMHO
far too small, especially since the consequences of overflow are so severe
(panic) x86-64 has the same problem because it shares this code.

This patch increases it to 64MB by default.

-Andi

diff -u linux/arch/ia64/lib/swiotlb.c-o linux/arch/ia64/lib/swiotlb.c
--- linux/arch/ia64/lib/swiotlb.c-o	2004-04-06 13:12:00.000000000 +0200
+++ linux/arch/ia64/lib/swiotlb.c	2004-06-24 21:04:08.000000000 +0200
@@ -44,7 +44,7 @@
 /*
  * log of the size of each IO TLB slab.  The number of slabs is command line controllable.
  */
-#define IO_TLB_SHIFT 11
+#define IO_TLB_SHIFT 16
 
 /*
  * Used to do a quick range check in swiotlb_unmap_single and swiotlb_sync_single_*, to see

Re: Increasing swiotlb default

[David Mosberger]

>>>>> On Thu, 24 Jun 2004 21:27:54 +0200, Andi Kleen <ak@suse.de> said:

  Andi> I discovered that swiotlb defaults to using only 2MB of RAM by
  Andi> default. That's IMHO far too small, especially since the
  Andi> consequences of overflow are so severe (panic) x86-64 has the
  Andi> same problem because it shares this code.

  Andi> This patch increases it to 64MB by default.

You haven't actually tested this, have you?  swiotlb.c has code which
assumes that IO_TLB_SHIFT <= PAGE_SHIFT.

Also, 64MB could be a fairly significant fraction of a system's memory.
Perhaps the default value should take the amount of system memory into
account?

	--david