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

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Message-ID: <4914ad9c-3eaf-b328-f31b-5d3077ef272f@arm.com>
Date:   Mon, 16 Mar 2020 15:37:23 +0000
From:   Vincenzo Frascino <vincenzo.frascino@....com>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     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>,
        Will Deacon <will@...nel.org>
Subject: Re: [PATCH v3 21/26] arm64: Introduce asm/vdso/arch_timer.h

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