From: Andrew Murray <andrew.murray@arm.com>
To: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: marc.zyngier@arm.com, catalin.marinas@arm.com,
will.deacon@arm.com, Andrew Morton <akpm@linux-foundation.org>,
rppt@linux.vnet.ibm.com, Michal Hocko <mhocko@suse.com>,
Ard Biesheuvel <ard.biesheuvel@linaro.org>,
james.morse@arm.com, sboyd@kernel.org,
linux-arm-kernel@lists.infradead.org,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v1 1/1] arm64: Early boot time stamps
Date: Tue, 20 Nov 2018 14:53:16 +0000 [thread overview]
Message-ID: <20181120145315.GA42987@e119886-lin.cambridge.arm.com> (raw)
In-Reply-To: <CA+CK2bAKcdZRRMwhcQ0QnBJ3_6bg=zhaeM7v74f+QFwkw9h17A@mail.gmail.com>
On Tue, Nov 20, 2018 at 09:40:10AM -0500, Pavel Tatashin wrote:
> > > +static __init void sched_clock_early_init(void)
> > > +{
> > > + u64 freq = arch_timer_get_cntfrq();
> > > + u64 (*read_time)(void) = arch_counter_get_cntvct;
> >
> > We already have arch_timer_read_counter which is exposed from
> > arm_arch_timer.h.
>
> OK
>
> >
> > > +
> > > + /* Early clock is available only on platforms with known freqs */
> >
> > This comment is misleading. It should read something like:
> >
> > /*
> > * The arm64 boot protocol mandates that CNTFRQ_EL0 reflects
> > * the timer frequency. To avoid breakage on misconfigured
> > * systems, do not register the early sched_clock if the
> > * programmed value if zero. Other random values will just
> > * result in random output.
> > */
> >
>
> OK
>
> > > + if (!freq)
> > > + return;
> > > +
> > > + sched_clock_register(read_time, BITS_PER_LONG, freq);
> >
> > This doesn't seem right. The counter has an architected minimum of 56
> > bits, and you can't assume that it is going to be more than that.
>
> Yeah, I saw 56 is used in arm_arch_timer.c, but I could not find where
> this minimum is defined in aarch64 specs. I will change it to 56.
See section G5.1.2 of the ARM ARM for details.
Thanks,
Andrew Murray
>
> I will send v2 soon.
>
> Thank you,
> Pasha
next prev parent reply other threads:[~2018-11-20 14:53 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-19 21:44 [PATCH v1 0/1] Early boot time stamps for arm64 Pavel Tatashin
2018-11-19 21:44 ` [PATCH v1 1/1] arm64: Early boot time stamps Pavel Tatashin
2018-11-20 11:29 ` Marc Zyngier
2018-11-20 14:40 ` Pavel Tatashin
2018-11-20 14:53 ` Andrew Murray [this message]
2018-11-20 14:55 ` Marc Zyngier
2018-11-20 15:03 ` Pavel Tatashin
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