From: catalin.marinas@arm.com (Catalin Marinas)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCHv5 16/16] clocksource: arch_timer: use virtual counters
Date: Thu, 31 Jan 2013 15:38:01 +0000 [thread overview]
Message-ID: <20130131153801.GM12877@arm.com> (raw)
In-Reply-To: <1359634539-9580-17-git-send-email-mark.rutland@arm.com>
On Thu, Jan 31, 2013 at 12:15:39PM +0000, Mark Rutland wrote:
> Switching between reading the virtual or physical counters is
> problematic, as some core code wants a view of time before we're fully
> set up. Using a function pointer and switching the source after the
> first read can make time appear to go backwards, and having a check in
> the read function is an unfortunate block on what we want to be a fast
> path.
>
> Instead, this patch makes us always use the virtual counters. If we're a
> guest, or don't have hyp mode, we'll use the virtual timers, and as such
> don't care about CNTVOFF as long as it doesn't change in such a way as
> to make time travel backwards. If we do have hyp mode, and might be a
> KVM host, we have to use the physical timers, and require CNTVOFF to be
> zero so as to have a consistent view of time between the physical timers
> and virtual counters.
>
> Any code which may want to alter CNTVOFF (e.g. KVM) will need to ensure
> that it is zeroed when entering the host.
>
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
next prev parent reply other threads:[~2013-01-31 15:38 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-31 12:15 [PATCHv5 00/16] Unify arm_generic and arch_timer drivers Mark Rutland
2013-01-31 12:15 ` [PATCHv5 01/16] arm: arch_timer: balance device_node refcounting Mark Rutland
2013-01-31 15:33 ` Catalin Marinas
2013-01-31 12:15 ` [PATCHv5 02/16] arm: arch_timer: remove redundant available check Mark Rutland
2013-01-31 12:15 ` [PATCHv5 03/16] arm: arch_timer: use u64/u32 for register data Mark Rutland
2013-01-31 12:15 ` [PATCHv5 04/16] arm: arch_timer: standardise counter reading Mark Rutland
2013-01-31 15:34 ` Catalin Marinas
2013-01-31 12:15 ` [PATCHv5 05/16] arm: arch_timer: split cntfrq accessor Mark Rutland
2013-01-31 12:15 ` [PATCHv5 06/16] arm: arch_timer: factor out register accessors Mark Rutland
2013-01-31 12:15 ` [PATCHv5 07/16] arm: arch_timer: add isbs to " Mark Rutland
2013-01-31 15:35 ` Catalin Marinas
2013-01-31 12:15 ` [PATCHv5 08/16] arm: arch_timer: divorce from local_timer api Mark Rutland
2013-01-31 12:15 ` [PATCHv5 09/16] arm: arch_timer: add arch_counter_set_user_access Mark Rutland
2013-01-31 15:36 ` Catalin Marinas
2013-01-31 12:15 ` [PATCHv5 10/16] arm: arch_timer: move core to drivers/clocksource Mark Rutland
2013-01-31 12:15 ` [PATCHv5 11/16] arm64: arm_generic: prevent reading stale time Mark Rutland
2013-01-31 15:36 ` Catalin Marinas
2013-01-31 12:15 ` [PATCHv5 12/16] arm64: move from arm_generic to arm_arch_timer Mark Rutland
2013-01-31 12:15 ` [PATCHv5 13/16] Documentation: Add ARMv8 to arch_timer devicetree Mark Rutland
2013-01-31 12:15 ` [PATCHv5 14/16] ARM: arch_timers: switch to physical timers if HYP mode is available Mark Rutland
2013-01-31 15:37 ` Catalin Marinas
2013-01-31 12:15 ` [PATCHv5 15/16] ARM: hyp: initialize CNTVOFF to zero Mark Rutland
2013-02-01 11:13 ` Dave Martin
2013-02-01 11:43 ` Marc Zyngier
2013-02-01 11:46 ` Mark Rutland
2013-02-01 18:07 ` Dave Martin
2013-02-04 9:29 ` Mark Rutland
2013-01-31 12:15 ` [PATCHv5 16/16] clocksource: arch_timer: use virtual counters Mark Rutland
2013-01-31 15:38 ` Catalin Marinas [this message]
2013-01-31 17:39 ` [PATCHv5 00/16] Unify arm_generic and arch_timer drivers Stephen Warren
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