On Wed, Sep 14, 2011 at 10:57 AM, Kyungmin Park kmpark@infradead.org wrote:
On Wed, Sep 14, 2011 at 4:43 PM, Siarhei Siamashka siarhei.siamashka@gmail.com wrote:
On Wed, Sep 14, 2011 at 9:08 AM, Kyungmin Park kmpark@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?
That's a good point. I think it is exynos4210 that is used in origenboard. And according to the value in Cache ID Register (0x4100c4c5), it has r3p0 revision of L2C-310. Which means that the Prefetch Control Register is actually described at: http://infocenter.arm.com/help/topic/com.arm.doc.ddi0246d/CHDHIECI.html And bit 27 is indeed reserved. However flipping it seems to have some measurable impact on performance (unless I screwed up the benchmarks), so maybe it does something but is undocumented? In any case, I agree that it's better not to mess up with this bit.
By the way, does anybody have L2C-310 errata list? Is double linefill actually safe to use in r3p0?