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Groups > linux.kernel > #1222501
| From | Guenter Roeck <linux@roeck-us.net> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH v7 5/8] Watchdog: introduce ARM SBSA watchdog driver |
| Date | 2015-09-11 05:00 +0200 |
| Message-ID | <q7mJb-5pm-5@gated-at.bofh.it> (permalink) |
| References | <pqlF8-659-23@gated-at.bofh.it> <q13pU-5xE-5@gated-at.bofh.it> <q13pV-5xE-43@gated-at.bofh.it> <q7iFz-6RE-17@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On 09/10/2015 03:29 PM, Jon Masters wrote: > On 08/24/2015 01:01 PM, fu.wei@linaro.org wrote: > >> + /* >> + * Get the frequency of system counter from the cp15 interface of ARM >> + * Generic timer. We don't need to check it, because if it returns "0", >> + * system would panic in very early stage. >> + */ >> + gwdt->clk = arch_timer_get_cntfrq(); > > Just thinking out loud... > > What happens later if we virtualize this device within KVM/QEMU/Xen and > then live migrate to another system in which the frequency changes? > Thinking about it, this scenario would cause severe trouble. I think clocks (like I would assume pretty much all other hardware parameters / registers) need to be virtualized and must not change. Example: clock is set to 100 kHz on original system, and 400 kHz on new system. Timeout is set to 30s, and registers are programmed accordingly. User space sends heartbeats every 15 seconds. In this scenario, the watchdog would time out after 30/4 = 7.5 seconds on the new system, or in other words almost immediately. This would be even worse if the original system had a clock of, say, 10 kHz and the new system would use 400 kHz. This just doesn't work. Guenter -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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Re: [PATCH v7 5/8] Watchdog: introduce ARM SBSA watchdog driver Jon Masters <jcm@redhat.com> - 2015-09-11 00:40 +0200
Re: [PATCH v7 5/8] Watchdog: introduce ARM SBSA watchdog driver Guenter Roeck <linux@roeck-us.net> - 2015-09-11 04:10 +0200
Re: [PATCH v7 5/8] Watchdog: introduce ARM SBSA watchdog driver Guenter Roeck <linux@roeck-us.net> - 2015-09-11 05:00 +0200
Re: [PATCH v7 5/8] Watchdog: introduce ARM SBSA watchdog driver Fu Wei <fu.wei@linaro.org> - 2015-09-14 19:20 +0200
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