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Re: [Qemu-devel] [PATCH] timer.h: Provide monotonic time for ARM guests
From: |
Peter Maydell |
Subject: |
Re: [Qemu-devel] [PATCH] timer.h: Provide monotonic time for ARM guests |
Date: |
Mon, 17 Apr 2017 19:42:08 +0100 |
On 15 April 2017 at 20:29, Pranith Kumar <address@hidden> wrote:
> Tested and confirmed that the stretch i386 debian qcow2 image on a
> raspberry pi 2 works.
>
> Fixes: LP#: 893208 <https://bugs.launchpad.net/qemu/+bug/893208/>
> Signed-off-by: Pranith Kumar <address@hidden>
> ---
> include/qemu/timer.h | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/include/qemu/timer.h b/include/qemu/timer.h
> index e1742f2f3d..14c9558da4 100644
> --- a/include/qemu/timer.h
> +++ b/include/qemu/timer.h
> @@ -1015,6 +1015,16 @@ static inline int64_t cpu_get_host_ticks(void)
> return cur - ofs;
> }
>
> +#elif defined(__arm__) || defined(__aarch64__)
> +
> +/* ARM does not have a user-space readble cycle counter available.
> + * This is a compromise to get monotonically increasing time.
> + */
> +static inline int64_t cpu_get_host_ticks(void)
> +{
> + return get_clock();
> +}
This doesn't look like it should be ARM-specific. Is it
better than the current default implementation? If so,
why not make this the default implementation?
> +
> #else
> /* The host CPU doesn't have an easily accessible cycle counter.
> Just return a monotonically increasing value. This will be
> --
> 2.11.0
The comment here says that our default is already a monotonically
increasing implementation -- is it wrong, or is there some other
advantage of your version?
thanks
-- PMM