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

[Wei Chen <Wei.Chen@xxxxxxx>]

Hi Julien,

> -----Original Message-----
> From: Julien Grall <julien.grall@xxxxxxx>
> Sent: 2018年7月9日 4:54
> To: Wei Chen <Wei.Chen@xxxxxxx>; minios-devel@xxxxxxxxxxxxxxxxxxxx;
> simon.kuenzer@xxxxxxxxx
> Cc: Kaly Xin <Kaly.Xin@xxxxxxx>; nd <nd@xxxxxxx>
> Subject: Re: [Minios-devel] [UNIKRAFT PATCHv4 23/43] plat/kvm: Add Arm64
> virtual timer library to provide ticks
> 
> Hi Wei,
> 
> On 07/06/2018 10:03 AM, Wei Chen wrote:
> > On KVM platform, print debug message will use ukplat_monotonic_clock
> > to provide timestamp. So we implement this simple virtual timer
> > library for timestamp.
> >
> > Signed-off-by: Wei Chen <Wei.Chen@xxxxxxx>
> > ---
> >   plat/kvm/arm/time.c | 127 ++++++++++++++++++++++++++++++++++++++++++++
> >   1 file changed, 127 insertions(+)
> >   create mode 100644 plat/kvm/arm/time.c
> >
> > 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.

> > @@ -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.

> 
> > + * comments.
> > + */
> > +static uint8_t tsc_shift;
> > +
> > +/* Multiplier for converting TSC ticks to nsecs. (0.S) fixed point. */
> > +static uint32_t ns_per_tick;
> > +
> > +/*
> > + * System Time
> > + * 64 bit value containing the nanoseconds elapsed since boot time.
> > + * This value is adjusted by frequency drift.
> > + * NOW() returns the current time.
> > + * The other macros are for convenience to approximate short intervals
> > + * of real time into system time
> 
> This looks like a copy of include/uk/arch/time.h. I don't really
> understand how this fit in the Arm context. For instance what does
> "frequency drift" stand on Arm?

I will remove this comment. This comment existed when I copy the template
from x86.

> 
> > + */
> > +#define NSEC_PER_SEC 1000000000ULL
> 
> It looks like to me this should go in common code.
> 
> > +
> > +static inline uint64_t ticks_to_ns(uint64_t ticks)
> > +{
> > +   return (ns_per_tick * ticks) >> tsc_shift;
> > +}
> > +
> > +static inline uint64_t get_counter_frequency(void)
> > +{
> > +   uint64_t frq;
> > +
> > +   __asm__ __volatile__("mrs %0, cntfrq_el0" : "=r" (frq):: "memory");
> > +
> > +   return frq;
> > +}
> 
> This should really be in a arch header and use SYSREG_READ.

OK

> 
> > +
> > +static inline uint64_t read_virtual_count(void)
> > +{
> > +   uint64_t val;
> > +
> > +   __asm__ __volatile__("mrs %0, cntvct_el0" : "=r" (val)::);
> > +   return val;
> > +}
> 
> Same here.
> 
> 
> > +
> > +/* monotonic_clock(): returns # of nanoseconds passed since time_init()
> 
> Coding style:
> 
> /*
>   * monotonic_clock ...
>   * ...
>   */
> > + * Note: This function is required to return accurate
> > + *       time even in the absence of multiple timer ticks.
> 
> I don't understand this comment.
> 

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.

> > + */
> > +__nsec ukplat_monotonic_clock(void)
> > +{
> > +   return (__nsec) ticks_to_ns(read_virtual_count() - cntvct_at_init);
> > +}
> > +
> > +void ukplat_time_init(void)
> > +{
> > +   /*
> > +    * Calculate TSC shift factor and scaling multiplier.
> > +    *
> > +    * tsc_shift (S) needs to be the largest (<=32) shift factor where the
> > +    * result of the tsc_mult calculcation below fits into uint32_t without
> 
> s/calculcation/calculation/
> 
> > +    * truncation. Note that we disallow an S of zero to ensure the loop
> always
> > +    * terminates.
> > +    *
> > +    * (0.S) tsc_mult = NSEC_PER_SEC (S.S) / tsc_freq (S.0)
> > +    */
> > +   uint64_t tmp;
> > +
> > +   counter_freq = get_counter_frequency();
> > +   tsc_shift = 32;
> > +   do {
> > +           tmp = (NSEC_PER_SEC << tsc_shift) / counter_freq;
> > +           if ((tmp & 0xFFFFFFFF00000000L) == 0L)
> > +                   ns_per_tick = (uint32_t)tmp;
> > +           else
> > +                   tsc_shift--;
> > +   } while (tsc_shift > 0 && ns_per_tick == 0L);
> > +#if 0 /* assert has been implemented for kvm */
> 
> The comment seems to contradict the implementation. So what's the state
> of assert? Looking at it, there seem to have a generic implementation
> for that.
> 

Ohh, it should be hasn't, sorry! When I enable the assert, the compiler
will get error when linking. I want place this assert to TODO list.


> > +   assert(ns_per_tick != 0L);
> > +#endif
> > +
> > +   /*
> > +    * Monotonic time begins at tsc_base (first read of TSC before
> 
> tsc_base is not defined here. Did you mean cntvct_at_init?

Yes. I implemented this library hurriedly, I would refine this library.

> 
> > +    * calibration).
> > +    */
> > +   cntvct_at_init = read_virtual_count();
> > +}
> > +
> > +void ukplat_time_fini(void)
> > +{
> > +   /* TODO */
> > +}
> >
> 
> Cheers,
> 
> --
> Julien Grall
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