Hi Al and Ola,
I have fixed the problem of mmap for STM, the kernel code is here [1], the user space example program is on linaro pastebin [2], I have tested the program on my device. If you have any questions, please let me know.
Thanks, Chunyan
[1] https://git.linaro.org/people/zhang.chunyan/linux.git/shortlog/refs/heads/st... [2] https://pastebin.linaro.org/view/21995dfa
On Fri, Apr 1, 2016 at 5:41 PM, Ola Liljedahl Ola.Liljedahl@arm.com wrote:
On 01/04/2016, 11:21, "CoreSight on behalf of Al Grant" <coresight-bounces@lists.linaro.org on behalf of Al.Grant@arm.com> wrote:
Ah, right, using this address (map) directly has some thing wrong for now, I haven't found the root cause. Now I have to focus the work on getting STM driver upstreamed first, and then I will take a look at what caused the problem. I will get back to you once STM mmap() interface works well.
Ok I look forward to it. I think a userspace write API could be quite useful for low-overhead instrumentation. On my Cortex-A57 server I can write a 32-bit STM timestamped data item, guaranteed delivery, from userspace every 30ns. It's not as fast as writing an untimestamped item to a ring buffer in local cache (~1ns) but it's less disruptive on cache, and a lot faster than calling clock_gettime() and writing a timestamped item to a ring buffer (~250ns). And I'm fairly sure that I could make the same API work on Intel STH too although I haven't got one to try out.
I approve of this.
‹ Ola
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