linux-kernel - Re: [PATCH v3 21/26] arm64: Introduce asm/vdso/arch

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Message-ID: <d578db85-7581-9bbb-2dab-25555e424ceb@arm.com>
Date:   Thu, 9 Apr 2020 14:36:48 +0100
From:   Vincenzo Frascino <vincenzo.frascino@....com>
To:     Will Deacon <will@...nel.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-mips@...r.kernel.org,
        clang-built-linux@...glegroups.com, x86@...nel.org,
        Will Deacon <will.deacon@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Russell King <linux@...linux.org.uk>,
        Paul Burton <paul.burton@...s.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Stephen Boyd <sboyd@...nel.org>,
        Mark Salyzyn <salyzyn@...roid.com>,
        Kees Cook <keescook@...omium.org>,
        Peter Collingbourne <pcc@...gle.com>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Andrei Vagin <avagin@...nvz.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Marc Zyngier <maz@...nel.org>,
        Mark Rutland <Mark.Rutland@....com>
Subject: Re: [PATCH v3 21/26] arm64: Introduce asm/vdso/arch_timer.h

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