Re: [PATCH]atomic_inc_return() for i386/x86_64 (Re: RCU issue with SELinux)

Re: [PATCH]atomic_inc_return() for i386/x86_64 (Re: RCU issue with SELinux)

[Andi Kleen]

"Kaigai Kohei" <kaigai@ak.jp.nec.com> writes:

> atomic_inc_return() is not defined for arm,arm26,i386,x86_64 and um archtectures.
> This attached patch adds atomic_inc_return() and atomic_dec_return() to arm,i386 and x86_64.
>
> It is implemented by 'xaddl' operation with LOCK prefix for i386 and x86_64.
> But this operation is permitted after i486 processor only.
> Another implementation may be necessary for i386SX/DX processor.
> But 'xaddl' operation is used in 'include/asm-i386/rwsem.h' unconditionally.
> I think it has agreed on using 'xaddl' operation in past days.

We don't support SMP on 386 boxes. What you can do for 386 is to use 
alternative() and just use an non SMP safe version for 386 and xadd 
for 486+ 

This will require adding a new pseudo CPUID bit in cpufeature.h 
that can be tested for in alternative (similar to the X86_FEATURE_P3/P4 
flags that are already there)

-Andi

Re: [PATCH]atomic_inc_return() for i386/x86_64 (Re: RCU issue with SELinux)

[Kaigai Kohei]

[-- Attachment #1: Type: text/plain, Size: 1484 bytes --]

Hi Andi, thanks for your comment.
Sorry, I have not noticed your mail in the flood of Linux-Kernel ML.

> > atomic_inc_return() is not defined for arm,arm26,i386,x86_64 and um archtectures.
> > This attached patch adds atomic_inc_return() and atomic_dec_return() to arm,i386 and x86_64.
> >
> > It is implemented by 'xaddl' operation with LOCK prefix for i386 and x86_64.
> > But this operation is permitted after i486 processor only.
> > Another implementation may be necessary for i386SX/DX processor.
> > But 'xaddl' operation is used in 'include/asm-i386/rwsem.h' unconditionally.
> > I think it has agreed on using 'xaddl' operation in past days.
> 
> We don't support SMP on 386 boxes. What you can do for 386 is to use 
> alternative() and just use an non SMP safe version for 386 and xadd 
> for 486+ 

We can avoid the problem by the simple solution, since SMP
on 386 boxes isn't supported. It is to disable interrupt
while updating atomic_t variable.

The attached patch modifies the include/asm-i386/atomic.h.
If the target processor is 386, then atomic_add_return() use
non-atomic operations between local_irq_disable() and local_irq_enable().
Otherwise, atomic_add_return() use 'xadd' operation with LOCK prefix.

By the way, do you know why 'xadd' operation is used
unconditionally in 'include/asm-i386/rwsem.h'?

Thanks.

Signed-off-by: KaiGai, Kohei <kaigai@ak.jp.nec.com>
Signed-off-by: Takayoshi Kochi <t-kochi@bq.jp.nec.com>
--------
Kai Gai <kaigai@ak.jp.nec.com>

[-- Attachment #2: atomic_inc_return-2.6.8.1.M386.patch --]
[-- Type: application/octet-stream, Size: 3067 bytes --]

--- linux-2.6.8.1/include/asm-arm/atomic.h	2004-08-14 19:54:50.000000000 +0900
+++ linux-2.6.8.1.rcu/include/asm-arm/atomic.h	2004-08-24 19:31:56.000000000 +0900
@@ -194,8 +194,10 @@
 #define atomic_dec(v)		atomic_sub(1, v)
 
 #define atomic_inc_and_test(v)	(atomic_add_return(1, v) == 0)
 #define atomic_dec_and_test(v)	(atomic_sub_return(1, v) == 0)
+#define atomic_inc_return(v)    (atomic_add_return(1, v))
+#define atomic_dec_return(v)    (atomic_sub_return(1, v))
 
 #define atomic_add_negative(i,v) (atomic_add_return(i, v) < 0)
 
 /* Atomic operations are already serializing on ARM */
--- linux-2.6.8.1/include/asm-i386/atomic.h	2004-08-14 19:55:09.000000000 +0900
+++ linux-2.6.8.1.rcu/include/asm-i386/atomic.h	2004-08-31 13:10:48.000000000 +0900
@@ -1,8 +1,9 @@
 #ifndef __ARCH_I386_ATOMIC__
 #define __ARCH_I386_ATOMIC__
 
 #include <linux/config.h>
+#include <asm/system.h>
 
 /*
  * Atomic operations that C can't guarantee us.  Useful for
  * resource counting etc..
@@ -175,8 +176,41 @@
 		:"ir" (i), "m" (v->counter) : "memory");
 	return c;
 }
 
+/**
+ * atomic_add_return - add and return
+ * @v: pointer of type atomic_t
+ * @i: integer value to add
+ *
+ * Atomically adds @i to @v and returns @i + @v
+ */
+static __inline__ int atomic_add_return(int i, atomic_t *v)
+{
+	int __i;
+#ifdef CONFIG_M386
+	local_irq_disable();
+	__i = atomic_read(v);
+	atomic_set(v, i + __i);
+	local_irq_enable();
+#else
+	__i = i;
+	__asm__ __volatile__(
+		LOCK "xaddl %0, %1;"
+		:"=r"(i)
+		:"m"(v->counter), "0"(i));
+#endif
+	return i + __i;
+}
+
+static __inline__ int atomic_sub_return(int i, atomic_t *v)
+{
+	return atomic_add_return(-i,v);
+}
+
+#define atomic_inc_return(v)  (atomic_add_return(1,v))
+#define atomic_dec_return(v)  (atomic_sub_return(1,v))
+
 /* These are x86-specific, used by some header files */
 #define atomic_clear_mask(mask, addr) \
 __asm__ __volatile__(LOCK "andl %0,%1" \
 : : "r" (~(mask)),"m" (*addr) : "memory")
--- linux-2.6.8.1/include/asm-x86_64/atomic.h	2004-08-14 19:56:23.000000000 +0900
+++ linux-2.6.8.1.rcu/include/asm-x86_64/atomic.h	2004-08-25 11:57:36.000000000 +0900
@@ -177,8 +177,33 @@
 		:"ir" (i), "m" (v->counter) : "memory");
 	return c;
 }
 
+/**
+ * atomic_add_return - add and return
+ * @v: pointer of type atomic_t
+ * @i: integer value to add
+ *
+ * Atomically adds @i to @v and returns @i + @v
+ */
+static __inline__ int atomic_add_return(int i, atomic_t *v)
+{
+	int __i = i;
+	__asm__ __volatile__(
+		LOCK "xaddl %0, %1;"
+		:"=r"(i)
+		:"m"(v->counter), "0"(i));
+	return i + __i;
+}
+
+static __inline__ int atomic_sub_return(int i, atomic_t *v)
+{
+	return atomic_add_return(-i,v);
+}
+
+#define atomic_inc_return(v)  (atomic_add_return(1,v))
+#define atomic_dec_return(v)  (atomic_sub_return(1,v))
+
 /* These are x86-specific, used by some header files */
 #define atomic_clear_mask(mask, addr) \
 __asm__ __volatile__(LOCK "andl %0,%1" \
 : : "r" (~(mask)),"m" (*addr) : "memory")

Re: [PATCH]atomic_inc_return() for i386/x86_64 (Re: RCU issue with SELinux)

[Andi Kleen]

On Tue, Aug 31, 2004 at 05:19:34PM +0900, Kaigai Kohei wrote:
> Hi Andi, thanks for your comment.
> Sorry, I have not noticed your mail in the flood of Linux-Kernel ML.
> 
> > > atomic_inc_return() is not defined for arm,arm26,i386,x86_64 and um archtectures.
> > > This attached patch adds atomic_inc_return() and atomic_dec_return() to arm,i386 and x86_64.
> > >
> > > It is implemented by 'xaddl' operation with LOCK prefix for i386 and x86_64.
> > > But this operation is permitted after i486 processor only.
> > > Another implementation may be necessary for i386SX/DX processor.
> > > But 'xaddl' operation is used in 'include/asm-i386/rwsem.h' unconditionally.
> > > I think it has agreed on using 'xaddl' operation in past days.
> > 
> > We don't support SMP on 386 boxes. What you can do for 386 is to use 
> > alternative() and just use an non SMP safe version for 386 and xadd 
> > for 486+ 
> 
> We can avoid the problem by the simple solution, since SMP
> on 386 boxes isn't supported. It is to disable interrupt
> while updating atomic_t variable.

The patch is wrong.  A CONFIG_M386 kernel can run on non
386 SMP boxes. Your patch would be racy then. The only thing 
that's not supported is a real 386 with multiple CPUs.

You either have to check boot_cpu_data.x86 == 3 at runtime or 
use alternative() like I earlier suggested.

> By the way, do you know why 'xadd' operation is used
> unconditionally in 'include/asm-i386/rwsem.h'?

386 compatible kernels use a different rwsem implementation
that doesn't use this include.

-Andi

Re: [PATCH]atomic_inc_return() for i386/x86_64 (Re: RCU issue with SELinux)

[Kaigai Kohei]

[-- Attachment #1: Type: text/plain, Size: 945 bytes --]

Hi Andi, thanks for your comment.

> > We can avoid the problem by the simple solution, since SMP
> > on 386 boxes isn't supported. It is to disable interrupt
> > while updating atomic_t variable.
> 
> The patch is wrong.  A CONFIG_M386 kernel can run on non
> 386 SMP boxes. Your patch would be racy then. The only thing 
> that's not supported is a real 386 with multiple CPUs.
> 
> You either have to check boot_cpu_data.x86 == 3 at runtime or 
> use alternative() like I earlier suggested.

Indeed, the attached patch is implemented according to the suggestion.
The code for legacy-386 is used only when boot_cpu_data.x86 == 3.
This run-time check is done only when CONFIG_M386 is set.
Otherwise, we use 'XADD' operation for atomic_add_return()
as the previous patch.

I don't adopt the alternative(), because the macro doesn't fit for the situation
when arguments for __asm__ are necessary.

Thanks.
--------
Kai Gai <kaigai@ak.jp.nec.com>

[-- Attachment #2: atomic_inc_return-2.6.8.1.M386.patch --]
[-- Type: application/octet-stream, Size: 3270 bytes --]

--- linux-2.6.8.1/include/asm-i386/atomic.h	2004-08-14 19:55:09.000000000 +0900
+++ linux-2.6.8.1.rcu/include/asm-i386/atomic.h	2004-09-01 14:40:40.000000000 +0900
@@ -1,8 +1,10 @@
 #ifndef __ARCH_I386_ATOMIC__
 #define __ARCH_I386_ATOMIC__
 
 #include <linux/config.h>
+#include <linux/compiler.h>
+#include <asm/processor.h>
 
 /*
  * Atomic operations that C can't guarantee us.  Useful for
  * resource counting etc..
@@ -175,8 +177,48 @@
 		:"ir" (i), "m" (v->counter) : "memory");
 	return c;
 }
 
+/**
+ * atomic_add_return - add and return
+ * @v: pointer of type atomic_t
+ * @i: integer value to add
+ *
+ * Atomically adds @i to @v and returns @i + @v
+ */
+static __inline__ int atomic_add_return(int i, atomic_t *v)
+{
+	int __i;
+#ifdef CONFIG_M386
+	if(unlikely(boot_cpu_data.x86==3))
+		goto no_xadd;
+#endif
+	/* Modern 486+ processor */
+	__i = i;
+	__asm__ __volatile__(
+		LOCK "xaddl %0, %1;"
+		:"=r"(i)
+		:"m"(v->counter), "0"(i));
+	return i + __i;
+
+#ifdef CONFIG_M386
+no_xadd: /* Legacy 386 processor */
+	local_irq_disable();
+	__i = atomic_read(v);
+	atomic_set(v, i + __i);
+	local_irq_enable();
+	return i + __i;
+#endif
+}
+
+static __inline__ int atomic_sub_return(int i, atomic_t *v)
+{
+	return atomic_add_return(-i,v);
+}
+
+#define atomic_inc_return(v)  (atomic_add_return(1,v))
+#define atomic_dec_return(v)  (atomic_sub_return(1,v))
+
 /* These are x86-specific, used by some header files */
 #define atomic_clear_mask(mask, addr) \
 __asm__ __volatile__(LOCK "andl %0,%1" \
 : : "r" (~(mask)),"m" (*addr) : "memory")
--- linux-2.6.8.1/include/asm-x86_64/atomic.h	2004-08-14 19:56:23.000000000 +0900
+++ linux-2.6.8.1.rcu/include/asm-x86_64/atomic.h	2004-08-25 11:57:36.000000000 +0900
@@ -177,8 +177,33 @@
 		:"ir" (i), "m" (v->counter) : "memory");
 	return c;
 }
 
+/**
+ * atomic_add_return - add and return
+ * @v: pointer of type atomic_t
+ * @i: integer value to add
+ *
+ * Atomically adds @i to @v and returns @i + @v
+ */
+static __inline__ int atomic_add_return(int i, atomic_t *v)
+{
+	int __i = i;
+	__asm__ __volatile__(
+		LOCK "xaddl %0, %1;"
+		:"=r"(i)
+		:"m"(v->counter), "0"(i));
+	return i + __i;
+}
+
+static __inline__ int atomic_sub_return(int i, atomic_t *v)
+{
+	return atomic_add_return(-i,v);
+}
+
+#define atomic_inc_return(v)  (atomic_add_return(1,v))
+#define atomic_dec_return(v)  (atomic_sub_return(1,v))
+
 /* These are x86-specific, used by some header files */
 #define atomic_clear_mask(mask, addr) \
 __asm__ __volatile__(LOCK "andl %0,%1" \
 : : "r" (~(mask)),"m" (*addr) : "memory")
--- linux-2.6.8.1/include/asm-arm/atomic.h	2004-08-14 19:54:50.000000000 +0900
+++ linux-2.6.8.1.rcu/include/asm-arm/atomic.h	2004-08-24 19:31:56.000000000 +0900
@@ -194,8 +194,10 @@
 #define atomic_dec(v)		atomic_sub(1, v)
 
 #define atomic_inc_and_test(v)	(atomic_add_return(1, v) == 0)
 #define atomic_dec_and_test(v)	(atomic_sub_return(1, v) == 0)
+#define atomic_inc_return(v)    (atomic_add_return(1, v))
+#define atomic_dec_return(v)    (atomic_sub_return(1, v))
 
 #define atomic_add_negative(i,v) (atomic_add_return(i, v) < 0)
 
 /* Atomic operations are already serializing on ARM */

Re: RCU issue with SELinux (Re: SELINUX performance issues)

[James Morris]

On Tue, 24 Aug 2004, Kaigai Kohei wrote:

> o UNIXbench
> 
> * INDEX value comparison
>                                        2.6.8.1   2.6.8.1   2.6.8.1   2.6.8.1
>                                      (Disable)  (Enable)  (rwlock)     (RCU)
> Dhrystone 2 using register variables    268.9     268.8     269.2     269.0
> Double-Precision Whetstone               94.2      94.2      94.2      94.2
> Execl Throughput                        388.3     379.0     377.8     377.9 +
> File Copy 1024 bufsize 2000 maxblocks   606.6     526.6     515.6     504.8 *
> File Copy 256 bufsize 500 maxblocks     508.9     417.0     410.4     395.2 *
> File Copy 4096 bufsize 8000 maxblocks   987.1     890.4     876.0     857.9 *
> Pipe Throughput                         525.1     406.4     404.5     408.8 +
> Process Creation                        321.2     317.8     315.9     316.3 +
> Shell Scripts (8 concurrent)           1312.8    1276.2    1278.8    1282.8 +
> System Call Overhead                    467.1     468.7     464.1     467.2 +
>                                     ========================================
>      FINAL SCORE                        445.8     413.2     410.1     407.7

This benchmark somewhat characterizes 1P performance, and the ones I've 
marked with (*) get noticably worse with the RCU patch compared to the 
current locking scheme.  Tests marked (+) show no or insignificant 
improvement.

Might be useful to compare with the lmbench macrobenchmark, to see if it 
shows a similar pattern.

> o dbench [ 4 processes run parallely on 4-CPUs / 10 times trials ]
>                   ---- mean ----  - STD -
> 2.6.8.1(disable)  860.249 [MB/s]   44.683
> 2.6.8.1(enable)   714.254 [MB/s]   32.359
> 2.6.8.1(+rwlock)  767.904 [MB/s]   27.968
> 2.6.8.1(+RCU)     830.678 [MB/s]   16.352

Can you show the figures for 1 and 2 clients?

> In IA-32 or x86_64, can anybady implement atomic_inc_return()?
> If it can not, I'll try to make alternative macros or inline functions.

If you can get this done, it will be very useful, as I could allso run 
some benchmarks on my test systems.


- James
-- 
James Morris
<jmorris@redhat.com>






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[PATCH]atomic_inc_return() for i386/x86_64 (Re: RCU issue with SELinux)

[Kaigai Kohei]

[-- Attachment #1: Type: text/plain, Size: 963 bytes --]

Hi James, thanks for your comment.

> > In IA-32 or x86_64, can anybady implement atomic_inc_return()?
> > If it can not, I'll try to make alternative macros or inline functions.
>
> If you can get this done, it will be very useful, as I could allso run
> some benchmarks on my test systems.

atomic_inc_return() is not defined for arm,arm26,i386,x86_64 and um archtectures.
This attached patch adds atomic_inc_return() and atomic_dec_return() to arm,i386 and x86_64.

It is implemented by 'xaddl' operation with LOCK prefix for i386 and x86_64.
But this operation is permitted after i486 processor only.
Another implementation may be necessary for i386SX/DX processor.
But 'xaddl' operation is used in 'include/asm-i386/rwsem.h' unconditionally.
I think it has agreed on using 'xaddl' operation in past days.

Is it acceptable? Any comment please.

(*) The implementation for ARM is simple wrapper to atomic_add_return().
--------
Kai Gai <kaigai@ak.jp.nec.com>

[-- Attachment #2: atomic_inc_return-2.6.8.1.patch --]
[-- Type: application/octet-stream, Size: 2739 bytes --]

--- linux-2.6.8.1/include/asm-arm/atomic.h	2004-08-14 19:54:50.000000000 +0900
+++ linux-2.6.8.1.rcu/include/asm-arm/atomic.h	2004-08-24 19:31:56.000000000 +0900
@@ -194,8 +194,10 @@
 #define atomic_dec(v)		atomic_sub(1, v)
 
 #define atomic_inc_and_test(v)	(atomic_add_return(1, v) == 0)
 #define atomic_dec_and_test(v)	(atomic_sub_return(1, v) == 0)
+#define atomic_inc_return(v)    (atomic_add_return(1, v))
+#define atomic_dec_return(v)    (atomic_sub_return(1, v))
 
 #define atomic_add_negative(i,v) (atomic_add_return(i, v) < 0)
 
 /* Atomic operations are already serializing on ARM */
--- linux-2.6.8.1/include/asm-i386/atomic.h	2004-08-14 19:55:09.000000000 +0900
+++ linux-2.6.8.1.rcu/include/asm-i386/atomic.h	2004-08-25 11:57:08.000000000 +0900
@@ -175,8 +175,34 @@
 		:"ir" (i), "m" (v->counter) : "memory");
 	return c;
 }
 
+/**
+ * atomic_add_return - add and return
+ * @v: pointer of type atomic_t
+ * @i: integer value to add
+ *
+ * Atomically adds @i to @v and returns @i + @v
+ */
+static __inline__ int atomic_add_return(int i, atomic_t *v)
+{
+	/* NOTICE: This function can be used on i486+ */
+	int __i = i;
+	__asm__ __volatile__(
+		LOCK "xaddl %0, %1;"
+		:"=r"(i)
+		:"m"(v->counter), "0"(i));
+	return i + __i;
+}
+
+static __inline__ int atomic_sub_return(int i, atomic_t *v)
+{
+	return atomic_add_return(-i,v);
+}
+
+#define atomic_inc_return(v)  (atomic_add_return(1,v))
+#define atomic_dec_return(v)  (atomic_sub_return(1,v))
+
 /* These are x86-specific, used by some header files */
 #define atomic_clear_mask(mask, addr) \
 __asm__ __volatile__(LOCK "andl %0,%1" \
 : : "r" (~(mask)),"m" (*addr) : "memory")
--- linux-2.6.8.1/include/asm-x86_64/atomic.h	2004-08-14 19:56:23.000000000 +0900
+++ linux-2.6.8.1.rcu/include/asm-x86_64/atomic.h	2004-08-25 11:57:36.000000000 +0900
@@ -177,8 +177,33 @@
 		:"ir" (i), "m" (v->counter) : "memory");
 	return c;
 }
 
+/**
+ * atomic_add_return - add and return
+ * @v: pointer of type atomic_t
+ * @i: integer value to add
+ *
+ * Atomically adds @i to @v and returns @i + @v
+ */
+static __inline__ int atomic_add_return(int i, atomic_t *v)
+{
+	int __i = i;
+	__asm__ __volatile__(
+		LOCK "xaddl %0, %1;"
+		:"=r"(i)
+		:"m"(v->counter), "0"(i));
+	return i + __i;
+}
+
+static __inline__ int atomic_sub_return(int i, atomic_t *v)
+{
+	return atomic_add_return(-i,v);
+}
+
+#define atomic_inc_return(v)  (atomic_add_return(1,v))
+#define atomic_dec_return(v)  (atomic_sub_return(1,v))
+
 /* These are x86-specific, used by some header files */
 #define atomic_clear_mask(mask, addr) \
 __asm__ __volatile__(LOCK "andl %0,%1" \
 : : "r" (~(mask)),"m" (*addr) : "memory")