Re: [PATCHv2] powerpc: POWER8 memcpy optimization for cached memory

[Rajalakshmi Srinivasaraghavan <raji@linux.vnet.ibm.com>]

On 12/09/2017 01:10 AM, Tulio Magno Quites Machado Filho wrote:
> From: Adhemerval Zanella<azanella@linux.vnet.ibm.com>
> 
> I made the changes I requested, updated copyright entries, added a
> manual entry and fixed a build issue on powerpc64.
> 
> --- 8< ---
> 
> On POWER8, unaligned memory accesses to cached memory has little impact
> on performance as opposed to its ancestors.
> 
> It is disabled by default and will only be available when the tunable
> glibc.tune.cached_memopt is set to 1.
> 
>                   __memcpy_power8_cached      __memcpy_power7
> ============================================================
>      max-size=4096:     33325.70 ( 12.65%)        38153.00
>      max-size=8192:     32878.20 ( 11.17%)        37012.30
>     max-size=16384:     33782.20 ( 11.61%)        38219.20
>     max-size=32768:     33296.20 ( 11.30%)        37538.30
>     max-size=65536:     33765.60 ( 10.53%)        37738.40
> 
> 2017-12-08  Adhemerval Zanella<azanella@linux.vnet.ibm.com>
> 	    Tulio Magno Quites Machado Filho<tuliom@linux.vnet.ibm.com>
> 
> 	* manual/tunables.texi (Hardware Capability Tunables): Document
> 	glibc.tune.cached_memopt.
> 	* sysdeps/powerpc/cpu-features.c: New file.
> 	* sysdeps/powerpc/cpu-features.h: New file.
> 	* sysdeps/powerpc/dl-procinfo.c [!IS_IN(ldconfig)]: Add
> 	_dl_powerpc_cpu_features.
> 	* sysdeps/powerpc/dl-tunables.list: New file.
> 	* sysdeps/powerpc/ldsodefs.h: Include cpu-features.h.
> 	* sysdeps/powerpc/powerpc32/power4/multiarch/init-arch.h: .

Comment missing.
> 	* sysdeps/powerpc/powerpc64/dl-machine.h (INIT_ARCH): Initialize
> 	use_aligned_memopt.

Should this be moved to init-arch.h? (also use_cached_memopt)
> 	* sysdeps/powerpc/powerpc64/multiarch/Makefile (sysdep_routines):
> 	Add memcpy-power8-cached.
> 	* sysdeps/powerpc/powerpc64/multiarch/ifunc-impl-list.c: Add
> 	__memcpy_power8_cached.
> 	* sysdeps/powerpc/powerpc64/multiarch/memcpy.c: Likewise.
> 	* sysdeps/powerpc/powerpc64/multiarch/memcpy-power8-cached.S:
> 	New file.
> ---
> diff --git a/sysdeps/powerpc/powerpc64/multiarch/memcpy-power8-cached.S b/sysdeps/powerpc/powerpc64/multiarch/memcpy-power8-cached.S
> new file mode 100644
> index 0000000..e5b6f25
> --- /dev/null
> +++ b/sysdeps/powerpc/powerpc64/multiarch/memcpy-power8-cached.S
> @@ -0,0 +1,179 @@
> +	stxvd2x	v0,r0,r3
> +L(dst_is_align_16):
> +	cmpldi	cr7,r5,127
> +	ble	cr7,L(tail_copy)
> +	addi	r8,r5,-128
> +	mr	r9,r12
> +	rldicr	r8,r8,0,56
> +	li	r11,16
> +	srdi	r10,r8,7
> +	addi	r0,r8,128
> +	addi	r10,r10,1

Can we directly do
	rldicr  r0, r5, 0, 56
	srdi    r10,r5,7
instead of this sequence?
79         addi    r8,r5,-128
81         rldicr  r8,r8,0,56
83         srdi    r10,r8,7
84         addi    r0,r8,128
85         addi    r10,r10,1

> +	li	r6,32
> +	mtctr	r10
> +	li	r7,48
> +
> +	/* Main loop, copy 128 bytes each time.  */

LGTM.

Reviewed-by: Rajalakshmi Srinivasaraghavan  <raji@linux.vnet.ibm.com>


-- 
Thanks
Rajalakshmi S