linux-mips
[Top] [All Lists]

Re: Prefetches in memcpy

To: Dominic Sweetman <dom@algor.co.uk>
Subject: Re: Prefetches in memcpy
From: Carsten Langgaard <carstenl@mips.com>
Date: Thu, 05 Dec 2002 16:14:21 +0100
Cc: Ralf Baechle <ralf@uni-koblenz.de>, linux-mips@linux-mips.org, dom@mips.com, chris@mips.com, kevink@mips.com
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <3DC7CB8B.E2C1D4E5@mips.com> <20021105163806.A24996@bacchus.dhis.org> <3DEE19EC.DD007304@mips.com> <15855.7458.19248.593085@arsenal.algor.co.uk>
Sender: linux-mips-bounce@linux-mips.org
Here's what I think we should do for now (attached patch).

/Carsten


Dominic Sweetman wrote:

> Carsten,
>
> > I think we should get rid of the prefetches until someone comes up with a
> > version that doesn't prefetch beyond the copy destination/source area.
>
> I agree.
>
> --
> Dominic

--
_    _ ____  ___   Carsten Langgaard   Mailto:carstenl@mips.com
|\  /|||___)(___   MIPS Denmark        Direct: +45 4486 5527
| \/ |||    ____)  Lautrupvang 4B      Switch: +45 4486 5555
  TECHNOLOGIES     2750 Ballerup       Fax...: +45 4486 5556
                   Denmark             http://www.mips.com


Index: arch/mips/lib/memcpy.S
===================================================================
RCS file: /home/cvs/linux/arch/mips/lib/memcpy.S,v
retrieving revision 1.6.2.4
diff -u -r1.6.2.4 memcpy.S
--- arch/mips/lib/memcpy.S      19 Sep 2002 14:01:24 -0000      1.6.2.4
+++ arch/mips/lib/memcpy.S      5 Dec 2002 15:06:58 -0000
@@ -21,6 +21,17 @@
 #define src a1
 #define len a2
 
+/* 
+ * There is spread a number of PREF instructions in the memcpy function, but 
+ * there is no check if we are prefetching out-side the "memcpy" areas. 
+ * This is extremely dangerous because we might prefetch out-side the physical
+ * memory area causing e.g. a bus error or something even more nasty. 
+ * It could also hit a DMA buffer region, and there by break the PCI DMA 
+ * flushing scheme.
+ * So for now, we simply get rid of the PREFs here.
+ */
+#define PREF(hint,addr)
+       
 /*
  * Spec
  *
Index: arch/mips64/lib/memcpy.S
===================================================================
RCS file: /home/cvs/linux/arch/mips64/lib/memcpy.S,v
retrieving revision 1.9.2.3
diff -u -r1.9.2.3 memcpy.S
--- arch/mips64/lib/memcpy.S    19 Sep 2002 14:01:24 -0000      1.9.2.3
+++ arch/mips64/lib/memcpy.S    5 Dec 2002 15:06:59 -0000
@@ -21,6 +21,17 @@
 #define src a1
 #define len a2
 
+/* 
+ * There is spread a number of PREF instructions in the memcpy function, but 
+ * there is no check if we are prefetching out-side the "memcpy" areas. 
+ * This is extremely dangerous because we might prefetch out-side the physical
+ * memory area causing e.g. a bus error or something even more nasty. 
+ * It could also hit a DMA buffer region, and there by break the PCI DMA 
+ * flushing scheme.
+ * So for now, we simply get rid of the PREFs here.
+ */
+#define PREF(hint,addr)
+       
 /*
  * Spec
  *
<Prev in Thread] Current Thread [Next in Thread>