From: Sergei Shtylyov <sshtylyov@ru•mvista.com>
To: Paul Mackerras <paulus@samba•org>
Cc: linuxppc-dev@ozlabs•org, Thomas Gleixner <tglx@linutronix•de>,
Realtime Kernel <linux-rt-users@vger•kernel.org>
Subject: Re: [PATCH v2 3/4] Implement clockevents driver for powerpc
Date: Fri, 19 Oct 2007 15:49:37 +0400 [thread overview]
Message-ID: <471899D1.2000903@ru.mvista.com> (raw)
In-Reply-To: <18199.63230.583536.307945@cargo.ozlabs.ibm.com>
Hello.
Paul Mackerras wrote:
>>>What problem do you see arising from this?
>> Timers firing too early.
> Only if the minimum interrupt latency is less than 1 decrementer
> tick. That seems pretty unlikely to me unless you have a very slow
> timebase frequency.
Well, MPC8540 has 825 MHz CPU clock yet decrementor/timebase are clocked
with 25 MHz clock if I don't mistake. That gives us 33 CPU clocks of available
interrupt latency...
> In fact what we should program the decrementer to is:
> timeout - (is_booke? 0: 1) - min_interrupt_latency
BTW, why not handle the decrementer difference right in set_dec() where we
already have #ifdef'ed code?
> I was assuming that min_interrupt_latency (measured in timebase ticks)
> would be at least 1, but apparently some systems can have a timebase
> frequency as low as 1kHz, so we'll have to have an ifdef or something.
IMHO it's better to have #ifdef based on the decremeter model and forget
about the whole issue, rather than to #ifdef based on some bizarre system with
slowish decremeter, isn't it?
> Paul.
WBR, Sergei
next prev parent reply other threads:[~2007-10-19 11:49 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-09-21 3:26 [PATCH v2 1/4] Implement {read,update}_persistent_clock Tony Breeds
2007-09-21 3:26 ` [PATCH v2 2/4] Implement generic time of day clocksource for powerpc machines Tony Breeds
2007-09-21 4:05 ` Daniel Walker
2007-09-21 4:59 ` Paul Mackerras
2007-09-21 6:43 ` David Gibson
2007-09-21 4:52 ` Stephen Rothwell
2007-09-21 21:35 ` Tony Breeds
2007-09-21 21:35 ` [PATCH v3 " Tony Breeds
2007-10-03 0:48 ` Paul Mackerras
2007-10-03 4:00 ` Thomas Gleixner
2007-09-21 3:26 ` [PATCH v2 3/4] Implement clockevents driver for powerpc Tony Breeds
2007-10-15 17:40 ` Sergei Shtylyov
2007-10-15 18:33 ` Sergei Shtylyov
2007-10-15 23:44 ` Paul Mackerras
2007-10-17 14:29 ` Sergei Shtylyov
2007-10-18 0:51 ` Paul Mackerras
2007-10-18 15:11 ` Sergei Shtylyov
2007-10-19 1:53 ` Paul Mackerras
2007-10-19 12:11 ` Sergei Shtylyov
2007-10-19 12:36 ` Paul Mackerras
2007-10-19 13:35 ` Sergei Shtylyov
2007-10-24 12:07 ` Sergei Shtylyov
2007-10-24 23:55 ` Paul Mackerras
2007-10-17 14:34 ` Sergei Shtylyov
2007-10-18 0:36 ` Paul Mackerras
2007-10-18 14:48 ` Sergei Shtylyov
2007-10-19 0:14 ` Paul Mackerras
2007-10-19 9:22 ` Gabriel Paubert
2007-10-19 11:22 ` Paul Mackerras
2007-10-19 11:49 ` Sergei Shtylyov [this message]
2007-10-19 12:24 ` Paul Mackerras
2007-09-21 3:26 ` [PATCH v2 4/4] Enable tickless idle and high res timers " Tony Breeds
2007-09-26 19:04 ` [PATCH v2 1/4] Implement {read,update}_persistent_clock Steven Rostedt
2007-09-26 19:39 ` Sergei Shtylyov
2007-09-26 19:44 ` Steven Rostedt
2007-09-26 19:58 ` Thomas Gleixner
2007-10-15 18:05 ` Sergei Shtylyov
2007-10-15 23:46 ` Paul Mackerras
2007-10-16 1:19 ` Benjamin Herrenschmidt
2007-10-17 12:45 ` Sergei Shtylyov
2007-09-27 1:59 ` Benjamin Herrenschmidt
2007-10-15 18:07 ` Sergei Shtylyov
2007-10-15 23:02 ` Benjamin Herrenschmidt
2007-10-17 15:34 ` Sergei Shtylyov
2007-10-18 14:18 ` Sergei Shtylyov
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