Re: svn commit: r334712 - head/sys/compat/linuxkpi/common/include/asm

2018-06-06 Thread Hans Petter Selasky 

On 06/06/18 17:06, Mateusz Guzik wrote:

On Wed, Jun 6, 2018 at 3:59 PM, Hans Petter Selasky 
wrote:




cmpset loops are crap since they require an explicit re-read of the target
value

see fcmpset and refcount_acquire_if_not_zero for an example use



See r334718.

Thank you!

--HPS
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Re: svn commit: r334712 - head/sys/compat/linuxkpi/common/include/asm

2018-06-06 Thread Mateusz Guzik 
On Wed, Jun 6, 2018 at 3:59 PM, Hans Petter Selasky 
wrote:

> Author: hselasky
> Date: Wed Jun  6 13:59:51 2018
> New Revision: 334712
> URL: https://svnweb.freebsd.org/changeset/base/334712
>
> Log:
>   Implement the atomic_dec_if_positive() function in the LinuxKPI.
>
>   Submitted by: Johannes Lundberg 
>   MFC after:1 week
>   Sponsored by: Mellanox Technologies
>   Sponsored by: Limelight Networks
>
> Modified:
>   head/sys/compat/linuxkpi/common/include/asm/atomic.h
>
> Modified: head/sys/compat/linuxkpi/common/include/asm/atomic.h
> 
> ==
> --- head/sys/compat/linuxkpi/common/include/asm/atomic.hWed Jun
> 6 13:37:31 2018(r334711)
> +++ head/sys/compat/linuxkpi/common/include/asm/atomic.hWed Jun
> 6 13:59:51 2018(r334712)
> @@ -235,6 +235,22 @@ atomic_cmpxchg(atomic_t *v, int old, int new)
> __ret.val;  \
>  })
>
> +static inline int
> +atomic_dec_if_positive(atomic_t *v)
> +{
> +   int retval;
> +   int curr;
> +
> +   do {
> +   curr = atomic_read(v);
> +   retval = curr - 1;
> +   if (unlikely(retval < 0))
> +   break;
> +   } while (!likely(atomic_cmpset_int(>counter, curr, retval)));
> +
> +   return (retval);
> +}
> +
>

cmpset loops are crap since they require an explicit re-read of the target
value

see fcmpset and refcount_acquire_if_not_zero for an example use

-- 
Mateusz Guzik 
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svn commit: r334712 - head/sys/compat/linuxkpi/common/include/asm

2018-06-06 Thread Hans Petter Selasky 
Author: hselasky
Date: Wed Jun  6 13:59:51 2018
New Revision: 334712
URL: https://svnweb.freebsd.org/changeset/base/334712

Log:
  Implement the atomic_dec_if_positive() function in the LinuxKPI.
  
  Submitted by: Johannes Lundberg 
  MFC after:1 week
  Sponsored by: Mellanox Technologies
  Sponsored by: Limelight Networks

Modified:
  head/sys/compat/linuxkpi/common/include/asm/atomic.h

Modified: head/sys/compat/linuxkpi/common/include/asm/atomic.h
==
--- head/sys/compat/linuxkpi/common/include/asm/atomic.hWed Jun  6 
13:37:31 2018(r334711)
+++ head/sys/compat/linuxkpi/common/include/asm/atomic.hWed Jun  6 
13:59:51 2018(r334712)
@@ -235,6 +235,22 @@ atomic_cmpxchg(atomic_t *v, int old, int new)
__ret.val;  \
 })
 
+static inline int
+atomic_dec_if_positive(atomic_t *v)
+{
+   int retval;
+   int curr;
+
+   do {
+   curr = atomic_read(v);
+   retval = curr - 1;
+   if (unlikely(retval < 0))
+   break;
+   } while (!likely(atomic_cmpset_int(>counter, curr, retval)));
+
+   return (retval);
+}
+
 #defineLINUX_ATOMIC_OP(op, c_op)   \
 static inline void atomic_##op(int i, atomic_t *v) \
 {  \
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