From: Finn Thain <fthain@linux-m68k.org>
To: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Cc: "Peter Maydell" <peter.maydell@linaro.org>,
qemu-devel@nongnu.org, "Laurent Vivier" <laurent@vivier.eu>,
"Greg Kurz" <groug@kaod.org>,
qemu-ppc@nongnu.org, "David Gibson" <david@gibson.dropbear.id.au>,
"Philippe Mathieu-Daudé" <f4bug@amsat.org>
Subject: Re: [RFC 00/10] hw/mos6522: VIA timer emulation fixes and improvements
Date: Wed, 1 Sep 2021 12:20:32 +1000 (AEST) [thread overview]
Message-ID: <6c8edbbb-1d2-ee8f-6550-ace8dea36599@linux-m68k.org> (raw)
In-Reply-To: <4da39536-1acb-05c3-755c-9a30d82d6ace@ilande.co.uk>
On Tue, 31 Aug 2021, Mark Cave-Ayland wrote:
> You mentioned that the OS may compensate for the fact that the 6522
> doesn't have an overflow flag: can you explain more as to how this works
> in Linux?
When running on real hardware, Linux/mac68k does so by
- Elevating the interrupt priority of VIA 1 so that other drivers do not
interfere with timekeeping
- Constraining intervals during which the IPL is kept elevated (i.e.
local_irq_disable/enable).
When runing on QEMU, none of that is sufficient and the Linux/mac68k
kernel can do very little to influence interrupt latency.
Linux ports to other platforms typically have multiple timers and counters
with which to implement reliable clocksource devices.
When running on other virtualization platforms, Linux may solve the
problem using a paravirtual clock device. Please see
CONFIG_PARAVIRT_CLOCK, arch/x86/include/asm/pvclock-abi.h,
arch/x86/kernel/pvclock.c, arch/x86/include/asm/vdso/gettimeofday.h
arch/x86/xen/time.c and so on.
next prev parent reply other threads:[~2021-09-01 2:38 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-24 10:09 [RFC 00/10] hw/mos6522: VIA timer emulation fixes and improvements Finn Thain
2021-08-24 10:09 ` [RFC 09/10] hw/mos6522: Avoid using discrepant QEMU clock values Finn Thain
2021-08-24 10:28 ` Philippe Mathieu-Daudé
2021-08-29 1:23 ` Finn Thain
2021-08-25 8:44 ` Mark Cave-Ayland
2021-08-29 1:55 ` Finn Thain
2021-08-24 10:09 ` [RFC 06/10] hw/mos6522: Implement oneshot mode Finn Thain
2021-08-25 8:18 ` Mark Cave-Ayland
2021-08-29 1:20 ` Finn Thain
2021-08-24 10:09 ` [RFC 01/10] hw/mos6522: Remove get_load_time() methods and functions Finn Thain
2021-08-24 10:29 ` Philippe Mathieu-Daudé
2021-08-25 6:55 ` Mark Cave-Ayland
2021-08-28 1:00 ` Finn Thain
2021-08-24 10:09 ` [RFC 08/10] hw/mos6522: Call mos6522_update_irq() when appropriate Finn Thain
2021-08-24 10:22 ` Philippe Mathieu-Daudé
2021-08-25 8:26 ` Mark Cave-Ayland
2021-08-24 10:09 ` [RFC 07/10] hw/mos6522: Fix initial timer counter reload Finn Thain
2021-08-25 8:23 ` Mark Cave-Ayland
2021-08-28 0:46 ` Finn Thain
2021-08-24 10:09 ` [RFC 10/10] hw/mos6522: Synchronize timer interrupt and timer counter Finn Thain
2021-08-25 8:52 ` Mark Cave-Ayland
2021-08-26 6:43 ` Finn Thain
2021-08-24 10:09 ` [RFC 04/10] hw/mos6522: Rename timer callback functions Finn Thain
2021-08-24 10:28 ` Philippe Mathieu-Daudé
2021-08-25 7:11 ` Mark Cave-Ayland
2021-08-26 7:42 ` Philippe Mathieu-Daudé
2021-08-24 10:09 ` [RFC 02/10] hw/mos6522: Remove get_counter_value() methods and functions Finn Thain
2021-08-24 10:29 ` Philippe Mathieu-Daudé
2021-08-24 10:09 ` [RFC 05/10] hw/mos6522: Don't clear T1 interrupt flag on latch write Finn Thain
2021-08-25 7:20 ` Mark Cave-Ayland
2021-08-26 5:21 ` Finn Thain
2021-09-01 14:32 ` Laurent Vivier
2021-09-01 22:26 ` Finn Thain
2021-08-24 10:09 ` [RFC 03/10] hw/mos6522: Remove redundant mos6522_timer1_update() calls Finn Thain
2021-08-25 7:09 ` Mark Cave-Ayland
2021-08-24 10:34 ` [RFC 00/10] hw/mos6522: VIA timer emulation fixes and improvements Philippe Mathieu-Daudé
2021-08-28 1:22 ` Finn Thain
2021-08-31 21:14 ` Mark Cave-Ayland
2021-08-31 22:44 ` Finn Thain
2021-09-01 7:57 ` Mark Cave-Ayland
2021-09-01 8:06 ` Mark Cave-Ayland
2021-09-10 17:29 ` Mark Cave-Ayland
2021-09-11 0:08 ` Finn Thain
2021-09-01 2:20 ` Finn Thain [this message]
2021-08-25 3:11 ` David Gibson
2021-08-25 9:10 ` Mark Cave-Ayland
2021-08-28 4:11 ` Finn Thain
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