lkml.org 
[lkml]   [2003]   [Oct]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patches in this message
/
Date
From
SubjectRe: FEATURE REQUEST: Specific Processor Optimizations on x86 Architecture

On 10.24, Ingo Oeser wrote:
> Hi James,
>
> On Friday 24 October 2003 01:05, J.A. Magallon wrote:
> > There are some other specific code that could be used in the kernel,
> > for example mb() and so on can be implemented with {m,s,l}fence in p3/p4
> > processors, instead of the old 'lock; insn' (attached also).
>
> The sfence part might be ok (modulo errata not known to me), but
> replacing "This Barrier not needed on x86" with an instruction means,
> that either these instructions are NOPs or we have a real BUG there.
>
> Not using these mfence and lfence insn would mean less instructions,
> which is a good kernel optimization anyway ;-)
>
> Puzzled
>

Patch inlined. Credits should go to Zwane Mwaikambo <zwane@linux.realnet.co.sz>.
It adds the corresponding flags for PII) and P4, and in case thei are defined,
the *fence insn are used.

Included is also one other patch by Zwane, which states that smp_call_function
needs mb() instead of wmb().

I use them regularly, so they look safe. Are they really better ? At least they
do not touch any register, like the trick used till now.

22-x86-mb:

--- linux-2.4.21-pre5-jam1/arch/i386/config.in.orig 2003-03-07 03:50:19.000000000 +0100
+++ linux-2.4.21-pre5-jam1/arch/i386/config.in 2003-03-07 03:50:47.000000000 +0100
@@ -113,6 +113,7 @@
define_bool CONFIG_X86_PGE y
define_bool CONFIG_X86_USE_PPRO_CHECKSUM y
define_bool CONFIG_X86_F00F_WORKS_OK y
+ define_bool CONFIG_X86_SFENCE y
fi
if [ "$CONFIG_MPENTIUM4" = "y" ]; then
define_int CONFIG_X86_L1_CACHE_SHIFT 7
@@ -121,6 +122,9 @@
define_bool CONFIG_X86_PGE y
define_bool CONFIG_X86_USE_PPRO_CHECKSUM y
define_bool CONFIG_X86_F00F_WORKS_OK y
+ define_bool CONFIG_X86_SFENCE y
+ define_bool CONFIG_X86_LFENCE y
+ define_bool CONFIG_X86_MFENCE y
fi
if [ "$CONFIG_MK6" = "y" ]; then
define_int CONFIG_X86_L1_CACHE_SHIFT 5
--- linux-2.4.21-pre5-jam1/include/asm-i386/system.h.orig 2003-03-07 03:51:31.000000000 +0100
+++ linux-2.4.21-pre5-jam1/include/asm-i386/system.h 2003-03-07 03:51:40.000000000 +0100
@@ -290,16 +290,33 @@
*
* Some non intel clones support out of order store. wmb() ceases to be a
* nop for these.
+ *
+ * Pentium III introduced the SFENCE instruction for serialising all store
+ * operations, Pentium IV further introduced LFENCE and MFENCE for load and
+ * memory barriers respecively.
*/
-
+
+#ifdef CONFIG_X86_MFENCE
+#define mb() __asm__ __volatile__ ("mfence": : :"memory")
+#else
#define mb() __asm__ __volatile__ ("lock; addl $0,0(%%esp)": : :"memory")
+#endif
+
+#ifdef CONFIG_X86_LFENCE
+#define rmb() __asm__ __volatile__ ("lfence": : :"memory")
+#else
#define rmb() mb()
+#endif

+#ifdef CONFIG_X86_SFENCE
+#define wmb() __asm__ __volatile__ ("sfence": : :"memory")
+#else
#ifdef CONFIG_X86_OOSTORE
#define wmb() __asm__ __volatile__ ("lock; addl $0,0(%%esp)": : :"memory")
#else
#define wmb() __asm__ __volatile__ ("": : :"memory")
#endif
+#endif /* CONFIG_X86_SFENCE */

#ifdef CONFIG_SMP
#define smp_mb() mb()
009-smp-call-mb:

diff -u -p -B -r1.2 smp.c
--- linux-2.4.20/arch/i386/kernel/smp.c 11 Apr 2003 13:44:11 -0000 1.2
+++ linux-2.4.20/arch/i386/kernel/smp.c 11 Apr 2003 13:44:27 -0000
@@ -553,7 +553,7 @@ int smp_call_function (void (*func) (voi

spin_lock(&call_lock);
call_data = &data;
- wmb();
+ mb();
/* Send a message to all other CPUs and wait for them to respond */
send_IPI_allbutself(CALL_FUNCTION_VECTOR);

--
J.A. Magallon <jamagallon()able!es> \ Software is like sex:
werewolf!able!es \ It's better when it's free
Mandrake Linux release 9.2 (Cooker) for i586
Linux 2.4.23-pre8-jam1 (gcc 3.3.1 (Mandrake Linux 9.2 3.3.1-4mdk))
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:58    [W:0.581 / U:0.624 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site