Re: [PATCH v3 21/26] arm64: Introduce asm/vdso/arch_timer.h

Vincenzo Frascino
2020-04-09T13:36:08Z

Hi Will,

On 4/9/20 2:26 PM, Will Deacon wrote:
> Hi Vincenzo,
>
> Sorry, I was on holiday when you posted this and it slipped through the
> cracks.
>

No issue at all. Thank you for getting back to me.

> On Mon, Mar 16, 2020 at 03:37:23PM +0000, Vincenzo Frascino wrote:
>>> On Fri, Mar 13, 2020 at 03:43:40PM +0000, Vincenzo Frascino wrote:
>>>> The vDSO library should only include the necessary headers required for
>>>> a userspace library (UAPI and a minimal set of kernel headers). To make
>>>> this possible it is necessary to isolate from the kernel headers the
>>>> common parts that are strictly necessary to build the library.
>>>>
>>>> Introduce asm/vdso/arch_timer.h to contain all the arm64 specific
>>>> code. This allows to replace the second isb() in __arch_get_hw_counter()
>>>> with a fake dependent stack read of the counter which improves the vdso
>>>> library peformances of ~4.5%. Below the results of vdsotest [1] ran for
>>>> 100 iterations.
>>>
>>> The subject seems to imply a non-functional change but as you read, it
>>> gets a lot more complicated. Could you keep the functional change
>>> separate from the header clean-up, maybe submit it as an independent
>>> patch? And it shouldn't go in without Will's ack ;).
>>>
>>
>> It is fine by me. I will repost the series with the required fixes and without
>> this patch. This will give to me enough time to address Mark's comments as well
>> and to Will to have a proper look.
>
> Please can you post whatever is left at -rc1? I'll have a look then, but
> let's stick to just moving code around rather than randomly changing it
> at the same time, ok?
>

Sure, I will try to re-post it by -rc1 and take on board your comments.

> Thanks,
>
> Will
>

--
Regards,
Vincenzo