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

Vincenzo Frascino
2020-03-16T15:37:02Z

Hi Catalin,

On 3/15/20 6:32 PM, Catalin Marinas 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.

--
Regards,
Vincenzo