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Re: [PATCH 6/6] aarch64: Add hp-timing.h
- From: Marcus Shawcroft <marcus dot shawcroft at gmail dot com>
- To: Andrew Pinski <pinskia at gmail dot com>
- Cc: Richard Henderson <rth at twiddle dot net>, Andreas Schwab <schwab at suse dot de>, "libc-alpha at sourceware dot org" <libc-alpha at sourceware dot org>, "azanella at linux dot vnet dot ibm dot com" <azanella at linux dot vnet dot ibm dot com>, "davem at davemloft dot net" <davem at davemloft dot net>, "marcus dot shawcroft at arm dot com" <marcus dot shawcroft at arm dot com>
- Date: Tue, 22 Jul 2014 10:38:53 +0100
- Subject: Re: [PATCH 6/6] aarch64: Add hp-timing.h
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- References: <1403735086-21797-1-git-send-email-rth at twiddle dot net> <1403735086-21797-7-git-send-email-rth at twiddle dot net> <mvmd2czlz0k dot fsf at hawking dot suse dot de> <812AFAEE-C8E5-4583-8647-7E5ABE02F95C at gmail dot com> <mvm4myanco3 dot fsf at hawking dot suse dot de> <CAFqB+PyCXom3fqF8A=C10jV9syUeRmOg-JuTL1pxtVnLsgfj7A at mail dot gmail dot com> <53CD6492 dot 9080109 at twiddle dot net> <CA+=Sn1kTxPDb-zuAbvJYBG3hFS4qN=imx0ZF58Eaq3A1KfX9ZA at mail dot gmail dot com>
> On Mon, Jul 21, 2014 at 12:05 PM, Richard Henderson <rth@twiddle.net> wrote:
> Do you know of any real hardware that doesn't have the timers? I really can't
> imagine them being elided.
I'd like to see the generic timers none optional in cortex-a class
processors, however they are currently, unfortunately, defined as
optional. The design choices made in the first few instances of armv8
hardware are not necessarily a good basis for predicting the variety
of design choices that will follow in subsequent implementations.
> On 21 July 2014 21:42, Andrew Pinski <pinskia@gmail.com> wrote:
> More than that, right now the Linux kernel requires the timings so it
> is not optional for the linux kernel.
> http://lists.infradead.org/pipermail/linux-arm-kernel/2012-August/114155.html
>
> That patch makes it sound like it is part of the kernel userland
> ABI/API as it allows for a fast gettimeofday() (that does not have to
> be in VDSO if I read the comment correctly).
The counter is for the benefit of the VDSO in order for the VDSO to
provide a fast gettimeofday on systems where the counter is present.
Cheers
/Marcus