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From: Paolo Bonzini <pbonzini@redhat.com>
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Date: Tue, 6 Oct 2015 15:10:21 +0200
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Subject: Re: [Qemu-devel] [PATCH] target-arm: Use common CPU cycle
 infrastructure
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To: Peter Maydell <peter.maydell@linaro.org>
Cc: "qemu-devel@nongnu.org Developers" <qemu-devel@nongnu.org>, Laurent Vivier <lvivier@redhat.com>, Peter Crosthwaite <crosthwaitepeter@gmail.com>, Christopher Covington <cov@codeaurora.org>, Alistair Francis <alistair.francis@xilinx.com>



On 06/10/2015 15:06, Peter Maydell wrote:
> Looking closer, clock_gettime() also has a userspace
> only fastpath in the VDSO.

Yup, hence the patch that changed the default cpu_get_real_ticks()
implementation to get_clock().

>> > Could we just use CNTVCT_EL0?  Which cores have it?
>
> Not guaranteed to be enabled for userspace access by the kernel,
> and even if it is enabled, the kernel folks don't (last time I
> checked) consider this userspace ABI -- it's only there for
> the benefit of the VDSO.

Ok, thanks.

> (CNTVCT_EL0 is how the fast clock_gettime
> and getimeofday paths are implemented.)

Yes.

Paolo