From: George Anzinger <george@mvista.com>
To: dwalker@mvista.com
Cc: tglx@linutronix.de, john stultz <johnstul@us.ibm.com>,
Nish Aravamudan <nish.aravamudan@gmail.com>,
Ingo Molnar <mingo@elte.hu>,
linux-kernel@vger.kernel.org,
Steven Rostedt <rostedt@goodmis.org>,
"'high-res-timers-discourse@lists.sourceforge.net'"
<high-res-timers-discourse@lists.sourceforge.net>
Subject: Re: 2.6.13-rt6, ktimer subsystem
Date: Thu, 15 Sep 2005 17:08:33 -0700 [thread overview]
Message-ID: <432A0D01.7010303@mvista.com> (raw)
In-Reply-To: <1126825796.4576.31.camel@dhcp153.mvista.com>
Daniel Walker wrote:
> On Thu, 2005-09-15 at 15:35 -0700, George Anzinger wrote:
>
>>In the early HRT patches the whole timer list was replaced with a hashed
>>list. It was O(N/M) on insertion where we could easily choose M (for a
>>while it was even a config option). Removal was just an unlink, same as
>>the cascade list.
>>
>>To be clear on my take on this, as I understand it the rblist is
>>something like O(N*somelog 2). What is left out here is the fixed
>>overhead of F which is there even if N = 1. So we have something like
>>(F+O(f(N)) for a list. For the most part we don't look at F, but as
>>list complexity grows, it gets larger thus pushing out the cross over
>>point to a higher "N" when comparing two lists. I considered the rbtree
>>when doing the secondary list for HRT and concluded that "N" was small
>>enough that a simple O(N/2) list would do just fine as it would only
>>contain timers set to expire in the next jiffie.
>
>
> The fact that we know in advance that a system is only going to a very
> small number of these timers should be noted. You could just use a
> regular list , and limit the total number of timers . I would hesitate
> to stick a big data structure in when your only dealing with one or two
> timers on average..
>
> George, what's largest number of highres timers that someone might
> need/want?
>
Well, the interesting thing is that, unless you change something, the
system has a current limit of 1000 posix timers. This can be changed,
but, I suspect it is not changed very often. And this handles all posix
timers, low and high res. Sleep is another thing, with a max of one
sleep timer per task. The ktimer list is also doing itimers, which are
also limited to the number of tasks.
As for data structures, a hashed list requires a "list head" for each
bucket while, I think the rblist only has one list head, but requires an
additional list head (or is it two) in the entry data structure so this
is a pay as you go list.
--
George Anzinger george@mvista.com
HRT (High-res-timers): http://sourceforge.net/projects/high-res-timers/
next prev parent reply other threads:[~2005-09-16 0:09 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-09-13 10:00 2.6.13-rt6, ktimer subsystem Ingo Molnar
2005-09-13 19:59 ` Lee Revell
2005-09-13 20:06 ` Lee Revell
2005-09-13 20:10 ` Ingo Molnar
2005-09-13 20:36 ` Lee Revell
2005-09-15 7:55 ` Ingo Molnar
2005-09-15 11:37 ` Ingo Molnar
2005-09-14 15:56 ` Darren Hart
2005-09-14 22:09 ` Darren Hart
2005-09-14 19:38 ` George Anzinger
2005-09-15 2:25 ` Thomas Gleixner
2005-09-15 22:35 ` George Anzinger
2005-09-15 22:53 ` Thomas Gleixner
2005-09-15 23:10 ` George Anzinger
2005-09-15 23:09 ` Daniel Walker
2005-09-16 0:08 ` George Anzinger [this message]
2005-09-15 9:20 ` Ingo Molnar
2005-09-15 23:04 ` George Anzinger
2005-09-15 23:20 ` Thomas Gleixner
2005-09-15 9:43 ` Roman Zippel
2005-09-26 7:02 ` 2.6.14-rc2-rt2 Ingo Molnar
2005-09-27 6:13 ` 2.6.14-rc2-rt2 Eran Mann
2005-09-27 10:33 ` 2.6.14-rc2-rt2 Ingo Molnar
2005-09-27 16:59 ` 2.6.14-rc2-rt2 Fernando Lopez-Lezcano
2005-09-27 22:15 ` 2.6.14-rc2-rt2 Thomas Gleixner
2005-09-27 23:11 ` 2.6.14-rc2-rt2 Fernando Lopez-Lezcano
2005-09-27 23:10 ` 2.6.14-rc2-rt2 Daniel Walker
2005-09-28 3:04 ` 2.6.14-rc2-rt2 Fernando Lopez-Lezcano
2005-09-28 9:48 ` 2.6.14-rc2-rt2 Ingo Molnar
2005-09-28 16:34 ` 2.6.14-rc2-rt2 Fernando Lopez-Lezcano
2005-09-29 9:07 ` 2.6.14-rc2-rt2 Eran Mann
2005-09-28 9:10 ` 2.6.14-rc2-rt2 Peter Zijlstra
2005-09-29 16:45 ` 2.6.14-rc2-rt2 Badari Pulavarty
2005-09-30 10:58 ` 2.6.14-rc2-rt2 Ingo Molnar
2005-10-02 15:18 ` 2.6.14-rc3-rt1 Ingo Molnar
2005-10-02 15:42 ` 2.6.14-rc3-rt1 Mark Knecht
2005-10-02 19:25 ` 2.6.14-rc3-rt1 Mark Knecht
2005-10-06 17:13 ` 2.6.14-rc3-rt1 Steven Rostedt
2005-10-07 11:09 ` [patch] pcmcia-shutdown-fix.patch Ingo Molnar
2005-10-07 19:17 ` Russell King
2005-10-07 19:46 ` Steven Rostedt
2005-10-10 15:13 ` Steven Rostedt
2005-10-10 15:37 ` Steven Rostedt
2005-10-02 20:51 ` 2.6.14-rc3-rt1 Felix Oxley
2005-10-02 21:55 ` 2.6.14-rc3-rt1 Felix Oxley
2005-10-03 6:33 ` 2.6.14-rc3-rt1 Ingo Molnar
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