Re: [Minios-devel] [UNIKRAFT PATCHv4 23/43] plat/kvm: Add Arm64 virtual timer library to provide ticks

[Julien Grall <julien.grall@xxxxxxx>]

On 10/07/18 09:23, Wei Chen wrote:
> Hi Julien,
Hi Wei,

> > > diff --git a/plat/kvm/arm/time.c b/plat/kvm/arm/time.c
> > > new file mode 100644
> > > index 0000000..ab4968f
> > > --- /dev/null
> > > +++ b/plat/kvm/arm/time.c
> > The timer is generic on Arm. How about moving that to common arm64 code?
> I am re-implementing a timer library for Arm64 to support scheduler.
> Current timer library just to provide ukplat_monotonic_clock to
> make uk_printd can print timestamp.
>
> I will place the new library to common code.
You can probably place it in common Arm (32-bit and 64-bit) code.

> > > @@ -0,0 +1,127 @@
> > > +/* SPDX-License-Identifier: BSD-3-Clause */
> > Same remark as before for SPDX.
> >
> > > +/*
> > > + * Authors: Wei Chen <Wei.Chen@xxxxxxx>
> > > + *
> > > + * Copyright (c) 2018, Arm Ltd. All rights reserved.
> > > + *
> > > + * Redistribution and use in source and binary forms, with or without
> > > + * modification, are permitted provided that the following conditions
> > > + * are met:
> > > + *
> > > + * 1. Redistributions of source code must retain the above copyright
> > > + *    notice, this list of conditions and the following disclaimer.
> > > + * 2. Redistributions in binary form must reproduce the above copyright
> > > + *    notice, this list of conditions and the following disclaimer in the
> > > + *    documentation and/or other materials provided with the distribution.
> > > + * 3. Neither the name of the copyright holder nor the names of its
> > > + *    contributors may be used to endorse or promote products derived from
> > > + *    this software without specific prior written permission.
> > > + *
> > > + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
> > IS"
> > > + * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
> > THE
> > > + * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
> > PURPOSE
> > > + * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS
> > BE
> > > + * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
> > > + * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
> > > + * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
> > > + * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
> > > + * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
> > > + * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
> > THE
> > > + * POSSIBILITY OF SUCH DAMAGE.
> > > + *
> > > + * THIS HEADER MAY NOT BE EXTRACTED OR MODIFIED IN ANY WAY.
> > > + */
> > > +#include <stdlib.h>
> > > +#include <uk/assert.h>
> > > +#include <uk/plat/time.h>
> > > +
> > > +static uint64_t cntvct_at_init;
> > How about boot_ticks here?
> Not a big problem, OK.
>
> > > +static uint32_t counter_freq;
> > > +/*
> > > + * Shift factor for TSC scaling multiplier; referred to as S in the
> > following
> >
> > TSC has no meaning on Arm.
> Time Stamp Counter is a neutral word, I don't think it has obvious
> architecture characteristic. But if you think the abbreviation TSC
> is conflict/confused with x86's RDTSC, I would not use the abbreviation.
To be honest I never heard that word outside of x86 until your e-mail 
:). And wikipedia seems to disagree with you:
https://en.wikipedia.org/wiki/Time_Stamp_Counter

[...]

> I don't understand it either ; ) This comment existed in mini-os arm32
> timer originally. And have been copied to lots of projects, I just copied
> it from one of these projects.
My advice about Mini-OS arm32: Don't trust it! :)

Cheers,

--
Julien Grall

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