[RFC PATCH 2/2]powerpc: rewrite local_* to use CR5 flag
Gabriel Paubert
paubert at iram.es
Tue Dec 2 05:01:17 AEDT 2014
On Thu, Nov 27, 2014 at 05:48:41PM +0530, Madhavan Srinivasan wrote:
> This patch re-write the current local_* functions to CR5 based one.
> Base flow for each function is
>
> {
> set cr5(eq)
> load
> ..
> store
> clear cr5(eq)
> }
>
> Above set of instructions are followed by a fixup section which points
> to the entry of the function incase of interrupt in the flow. If the
> interrupt happens to be after the store, we just continue to last
> instruction in that block.
>
> Currently only asm/local.h has been rewrite, and local64 is TODO.
> Also the entire change is only for PPC64.
>
> Signed-off-by: Madhavan Srinivasan <maddy at linux.vnet.ibm.com>
> ---
> arch/powerpc/include/asm/local.h | 306 +++++++++++++++++++++++++++++++++++++++
> 1 file changed, 306 insertions(+)
>
> diff --git a/arch/powerpc/include/asm/local.h b/arch/powerpc/include/asm/local.h
> index b8da913..a26e5d3 100644
> --- a/arch/powerpc/include/asm/local.h
> +++ b/arch/powerpc/include/asm/local.h
> @@ -11,6 +11,310 @@ typedef struct
>
> #define LOCAL_INIT(i) { ATOMIC_LONG_INIT(i) }
>
> +#ifdef CONFIG_PPC64
> +
> +static __inline__ long local_read(local_t *l)
> +{
> + long t;
> +
> + __asm__ __volatile__(
> +"1: crset 22\n"
> +"2:" PPC_LL" %0,0(%1)\n"
> +"3: crclr 22\n"
> +"4:\n"
> +" .section __ex_table,\"a\"\n"
> + PPC_LONG_ALIGN "\n"
> + PPC_LONG "2b,1b\n"
> + PPC_LONG "3b,3b\n"
> +" .previous\n"
> + : "=&r" (t)
> + : "r" (&(l->a.counter)));
> +
> + return t;
> +}
> +
> +static __inline__ void local_set(local_t *l, long i)
> +{
> + long t;
> +
> + __asm__ __volatile__(
> +"1: crset 22\n"
> +"2:" PPC_LL" %0,0(%1)\n"
> +"3:" PPC405_ERR77(0,%2)
> +"4:" PPC_STL" %0,0(%2)\n"
> +"5: crclr 22\n"
> +"6:\n"
> +" .section __ex_table,\"a\"\n"
> + PPC_LONG_ALIGN "\n"
> + PPC_LONG "2b,1b\n"
> + PPC_LONG "3b,1b\n"
> + PPC_LONG "4b,1b\n"
> + PPC_LONG "5b,5b\n"
> +" .previous\n"
> + : "=&r" (t)
> + : "r" (&(i)), "r" (&(l->a.counter)));
> +}
> +
Apart from the other comments on bloat which can very likely
be removed by tracing backwards for a few instructions, removing
the exception table entries which are 2 or 4 (64 bit?) times as
large as the instruction sequence, I don't understand at all why
you need these sequences for the local_read and local_set functions.
After all these are single instructions (why do you perform a read before
the write in set when the result of the read is never used?).
I believe read and set are better mapped to access_once (or assign_once
or whatever it's called after the recent discussion on linux-kernel).
You don't even need a memory barrier if it's for a single thread,
so you could get away with a single volatile access to the variables.
For the other ones, I think that what you do is correct, except that
the workaround for PPC405 erratum 77 is not needed since this erratum
only affects the stwcx. instruction and the whole point of the patch
is to avoid the use of an l?arx/st?cx. pair.
Regards,
Gabriel
> +static __inline__ void local_add(long i, local_t *l)
> +{
> + long t;
> +
> + __asm__ __volatile__(
> +"1: crset 22\n"
> +"2:" PPC_LL" %0,0(%2)\n"
> +"3: add %0,%1,%0\n"
> +"4:" PPC405_ERR77(0,%2)
> +"5:" PPC_STL" %0,0(%2)\n"
> +"6: crclr 22\n"
> +"7:\n"
> +" .section __ex_table,\"a\"\n"
> + PPC_LONG_ALIGN "\n"
> + PPC_LONG "2b,1b\n"
> + PPC_LONG "3b,1b\n"
> + PPC_LONG "4b,1b\n"
> + PPC_LONG "5b,1b\n"
> + PPC_LONG "6b,6b\n"
> +" .previous\n"
> + : "=&r" (t)
> + : "r" (i), "r" (&(l->a.counter)));
> +}
> +
> +static __inline__ void local_sub(long i, local_t *l)
> +{
> + long t;
> +
> + __asm__ __volatile__(
> +"1: crset 22\n"
> +"2:" PPC_LL" %0,0(%2)\n"
> +"3: subf %0,%1,%0\n"
> +"4:" PPC405_ERR77(0,%2)
> +"5:" PPC_STL" %0,0(%2)\n"
> +"6: crclr 22\n"
> +"7:\n"
> +" .section __ex_table,\"a\"\n"
> + PPC_LONG_ALIGN "\n"
> + PPC_LONG "2b,1b\n"
> + PPC_LONG "3b,1b\n"
> + PPC_LONG "4b,1b\n"
> + PPC_LONG "5b,1b\n"
> + PPC_LONG "6b,6b\n"
> +" .previous\n"
> + : "=&r" (t)
> + : "r" (i), "r" (&(l->a.counter)));
> +}
> +
> +static __inline__ long local_add_return(long a, local_t *l)
> +{
> + long t;
> +
> + __asm__ __volatile__(
> +"1: crset 22\n"
> +"2:" PPC_LL" %0,0(%2)\n"
> +"3: add %0,%1,%0\n"
> +"4:" PPC405_ERR77(0,%2)
> +"5:" PPC_STL "%0,0(%2)\n"
> +"6: crclr 22\n"
> +"7:\n"
> +" .section __ex_table,\"a\"\n"
> + PPC_LONG_ALIGN "\n"
> + PPC_LONG "2b,1b\n"
> + PPC_LONG "3b,1b\n"
> + PPC_LONG "4b,1b\n"
> + PPC_LONG "5b,1b\n"
> + PPC_LONG "6b,6b\n"
> +" .previous\n"
> + : "=&r" (t)
> + : "r" (a), "r" (&(l->a.counter))
> + : "cc", "memory");
> +
> + return t;
> +}
> +
> +
> +#define local_add_negative(a, l) (local_add_return((a), (l)) < 0)
> +
> +static __inline__ long local_sub_return(long a, local_t *l)
> +{
> + long t;
> +
> + __asm__ __volatile__(
> +"1: crset 22\n"
> +"2:" PPC_LL" %0,0(%2)\n"
> +"3: subf %0,%1,%0\n"
> +"4:" PPC405_ERR77(0,%2)
> +"5:" PPC_STL "%0,0(%2)\n"
> +"6: crclr 22\n"
> +"7:\n"
> +" .section __ex_table,\"a\"\n"
> + PPC_LONG_ALIGN "\n"
> + PPC_LONG "2b,1b\n"
> + PPC_LONG "3b,1b\n"
> + PPC_LONG "4b,1b\n"
> + PPC_LONG "5b,1b\n"
> + PPC_LONG "6b,6b\n"
> +" .previous\n"
> + : "=&r" (t)
> + : "r" (a), "r" (&(l->a.counter))
> + : "cc", "memory");
> +
> + return t;
> +}
> +
> +static __inline__ long local_inc_return(local_t *l)
> +{
> + long t;
> +
> + __asm__ __volatile__(
> +"1: crset 22\n"
> +"2:" PPC_LL" %0,0(%1)\n"
> +"3: addic %0,%0,1\n"
> +"4:" PPC405_ERR77(0,%1)
> +"5:" PPC_STL "%0,0(%1)\n"
> +"6: crclr 22\n"
> +"7:\n"
> +" .section __ex_table,\"a\"\n"
> + PPC_LONG_ALIGN "\n"
> + PPC_LONG "2b,1b\n"
> + PPC_LONG "3b,1b\n"
> + PPC_LONG "4b,1b\n"
> + PPC_LONG "5b,1b\n"
> + PPC_LONG "6b,6b\n"
> +" .previous"
> + : "=&r" (t)
> + : "r" (&(l->a.counter))
> + : "cc", "xer", "memory");
> +
> + return t;
> +}
> +
> +/*
> + * local_inc_and_test - increment and test
> + * @l: pointer of type local_t
> + *
> + * Atomically increments @l by 1
> + * and returns true if the result is zero, or false for all
> + * other cases.
> + */
> +#define local_inc_and_test(l) (local_inc_return(l) == 0)
> +
> +static __inline__ long local_dec_return(local_t *l)
> +{
> + long t;
> +
> + __asm__ __volatile__(
> +"1: crset 22\n"
> +"2:" PPC_LL" %0,0(%1)\n"
> +"3: addic %0,%0,-1\n"
> +"4:" PPC405_ERR77(0,%1)
> +"5:" PPC_STL "%0,0(%1)\n"
> +"6: crclr 22\n"
> +"7:\n"
> +" .section __ex_table,\"a\"\n"
> + PPC_LONG_ALIGN "\n"
> + PPC_LONG "2b,1b\n"
> + PPC_LONG "3b,1b\n"
> + PPC_LONG "4b,1b\n"
> + PPC_LONG "5b,1b\n"
> + PPC_LONG "6b,6b\n"
> +" .previous\n"
> + : "=&r" (t)
> + : "r" (&(l->a.counter))
> + : "cc", "xer", "memory");
> +
> + return t;
> +}
> +
> +#define local_inc(l) local_inc_return(l)
> +#define local_dec(l) local_dec_return(l)
> +
> +#define local_cmpxchg(l, o, n) \
> + (cmpxchg_local(&((l)->a.counter), (o), (n)))
> +#define local_xchg(l, n) (xchg_local(&((l)->a.counter), (n)))
> +
> +/**
> + * local_add_unless - add unless the number is a given value
> + * @l: pointer of type local_t
> + * @a: the amount to add to v...
> + * @u: ...unless v is equal to u.
> + *
> + * Atomically adds @a to @l, so long as it was not @u.
> + * Returns non-zero if @l was not @u, and zero otherwise.
> + */
> +static __inline__ int local_add_unless(local_t *l, long a, long u)
> +{
> + long t;
> +
> + __asm__ __volatile__ (
> +"1: crset 22\n"
> +"2:" PPC_LL" %0,0(%1)\n"
> +"3: cmpw 0,%0,%3 \n"
> +"4: beq- 9f \n"
> +"5: add %0,%2,%0 \n"
> +"6:" PPC405_ERR77(0,%1)
> +"7:" PPC_STL" %0,0(%1) \n"
> +"8: subf %0,%2,%0 \n"
> +"9: crclr 22\n"
> +"10:\n"
> +" .section __ex_table,\"a\"\n"
> + PPC_LONG_ALIGN "\n"
> + PPC_LONG "2b,1b\n"
> + PPC_LONG "3b,1b\n"
> + PPC_LONG "4b,1b\n"
> + PPC_LONG "5b,1b\n"
> + PPC_LONG "6b,1b\n"
> + PPC_LONG "7b,1b\n"
> + PPC_LONG "8b,8b\n"
> + PPC_LONG "9b,9b\n"
> +" .previous\n"
> + : "=&r" (t)
> + : "r" (&(l->a.counter)), "r" (a), "r" (u)
> + : "cc", "memory");
> +
> + return t != u;
> +}
> +
> +#define local_inc_not_zero(l) local_add_unless((l), 1, 0)
> +
> +#define local_sub_and_test(a, l) (local_sub_return((a), (l)) == 0)
> +#define local_dec_and_test(l) (local_dec_return((l)) == 0)
> +
> +/*
> + * Atomically test *l and decrement if it is greater than 0.
> + * The function returns the old value of *l minus 1.
> + */
> +static __inline__ long local_dec_if_positive(local_t *l)
> +{
> + long t;
> +
> + __asm__ __volatile__(
> +"1: crset 22\n"
> +"2:" PPC_LL" %0,0(%1)\n"
> +"3: cmpwi %0,1\n"
> +"4: addi %0,%0,-1\n"
> +"5: blt- 8f\n"
> +"6:" PPC405_ERR77(0,%1)
> +"7:" PPC_STL "%0,0(%1)\n"
> +"8: crclr 22\n"
> +"9:\n"
> +" .section__ex_table,\"a\"\n"
> + PPC_LONG_ALIGN "\n"
> + PPC_LONG "2b,1b\n"
> + PPC_LONG "3b,1b\n"
> + PPC_LONG "4b,1b\n"
> + PPC_LONG "5b,1b\n"
> + PPC_LONG "6b,1b\n"
> + PPC_LONG "7b,1b\n"
> + PPC_LONG "8b,8b\n"
> +" .previous\n"
> + : "=&b" (t)
> + : "r" (&(l->a.counter))
> + : "cc", "memory");
> +
> + return t;
> +}
> +
> +#else
> +
> #define local_read(l) atomic_long_read(&(l)->a)
> #define local_set(l,i) atomic_long_set(&(l)->a, (i))
>
> @@ -162,6 +466,8 @@ static __inline__ long local_dec_if_positive(local_t *l)
> return t;
> }
>
> +#endif
> +
> /* Use these for per-cpu local_t variables: on some archs they are
> * much more efficient than these naive implementations. Note they take
> * a variable, not an address.
> --
> 1.9.1
>
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