[PATCH] ARM: EXYNOS4: Enable double linefill in PL310 Prefetch Control Register

[Kyungmin Park]

On Wed, Sep 14, 2011 at 4:43 PM, Siarhei Siamashka
<siarhei.siamashka at gmail.com> wrote:
> On Wed, Sep 14, 2011 at 9:08 AM, Kyungmin Park <kmpark at infradead.org> wrote:
>> Hi Siarhei,
>>
>> Interesting feature, and it's not samsung soc issue, so add the arm
>> mailing list.
>> It checked and the see the read performance improvement from 868MiB/s
>> to 981MiB/s with lmbench.
>
> Maybe lmbench does not try very hard to get the best out of the
> hardware? On my origenboard, I'm getting ~1.15GB/s performance for the
> standard LDM/STM based memcpy from libc-ports, which is ~2.3GB/s
> memory bandwidth if both reads and writes are accounted separately.
>
>> It's helpful to test other SoC., e.g., OMAP4, STE and so on.
>
> The current (?) state of the support for this feature in OMAP4 is
> explained here by Richard Woodruff:
>    http://groups.google.com/group/pandaboard/msg/dfd2d2e1336d435b
>
>> BTW, why do you set the 27-bit? In my PL310 Spec., it's reserved bit
>> and should be zero (SBZ).
>
> This PL310 thing seems to have been renamed to "CoreLink Level 2 Cache
> Controller L2C-310" in later revisions, and its Prefetch Control
> Register is described here:
>    http://infocenter.arm.com/help/topic/com.arm.doc.ddi0246f/CHDHIECI.html
Thanks for link. it has 27-bit description. but does it correct bit
description for exynos4 PL310?
I mean I received the PL310 TRM with exynos4 chip used. there's no
27-bit description. it's just reserved bit.
Can it enable the 27-bit at exynos4210? or can be used for exynos4212 or later?

Thank you,
Kyungmin Park
>
> Sorry for the confusing subject.
>
> Regarding bit 27 ('Double linefill on WRAP read disable'), it seems to
> reduce the impact of enabling double linefill on the random access
> latency as measured by my self-written simple memory benchmark
> program:
>    http://github.com/downloads/ssvb/ssvb-membench/ssvb-membench-0.1.tar.gz
>
> --
> Best regards,
> Siarhei Siamashka
>