Date:	Wed, 20 Sep 2006 12:50:03 -0400
From:	Gene Heskett <gene.heskett@...izon.net>
To:	linux-kernel@...r.kernel.org
Cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	John Stultz <johnstul@...ibm.com>,
	"Paul E. McKenney" <paulmck@...ibm.com>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: 2.6.18-rt1

On Wednesday 20 September 2006 10:19, Ingo Molnar wrote:
>I'm pleased to announce the 2.6.18-rt1 tree, which can be downloaded
>from the usual place:
>
>   http://redhat.com/~mingo/realtime-preempt/
>
>This port to the 2.6.18 codebase was very complex (given that 5 major
>features moved from -rt into 2.6.18: rtmutex, pi-futex, genirq, gtod and
>lockdep), so it took quite some time to finish, but in exchange it
>includes nice new features and also lots of bugfixes.
>
>In particular, a nasty softirq performance bug has been fixed, which
>caused the "5x slowdown under TCP" bug reported to lkml - those TCP
>performance figures are now on par with vanilla performance.
>
>The biggest new features are:
>
> - Dynticks (a tickless kernel). This is a new feature we implemented
>   ontop of hrtimers for the -hrt patchqueue and now we merged it to -rt
>   too. There's a new config option: CONFIG_NO_HZ, which if enabled,
>   produces a system with fewer timer interrupts. Currently i686 and
>   x86_64 are tested, but in general a hrtimers-ready platform needs
>   minimal changes to support dynticks too. (from Thomas Gleixner and
>   me, the x86_64 port is from Arjan van de Ven)
>
> - Timer expiry statistics feature from Thomas Gleixner:
>   CONFIG_TIMER_STATS. Enable/disable via "echo 1[0] > /proc/tstats",
>   display via "cat /proc/stats".
>
>   This kernel feature tracks the starting site (and expiry function) of
>   expired timers (both timer_list timers and hrtimers), and the number
>   of times they expired. This is a nice tool for those who'd like to
>   minimize the amount of timer ticks on their battery-based systems.
>   Sample output:
>
> Timerstats sample period: 3.888770 s
>   12,     0 swapper          hrtimer_stop_sched_tick
> (hrtimer_sched_tick) 15,     1 swapper          hcd_submit_urb
> (rh_timer_func)
>    4,   959 kedac            schedule_timeout (process_timeout)
>    1,     0 swapper          page_writeback_init (wb_timer_fn)
>   28,     0 swapper          hrtimer_stop_sched_tick
> (hrtimer_sched_tick) 22,  2948 IRQ 4            tty_flip_buffer_push
> (delayed_work_timer_fn) 3,  3100 bash             schedule_timeout
> (process_timeout) 1,     1 swapper          queue_delayed_work_on
> (delayed_work_timer_fn) 1,     1 swapper          queue_delayed_work_on
> (delayed_work_timer_fn) 1,     1 swapper         
> neigh_table_init_no_netlink (neigh_periodic_timer) 1,  2292 ip          
>     __netdev_watchdog_up (dev_watchdog) 1,    23 events/1        
> do_cache_clean (delayed_work_timer_fn) 90 total events, 30.0 events/sec
>
> - There's also a new runtime-configurable kernel option under
>   /proc/sys/kernel/timeout_granularity that allows the coarser expiry
>   of timer_list timers, and hence better batching of timer expiry.
>   (hrtimers are not affected) The value of this option gives a
>   'multiplier' to the standard HZ granularity.
>
> - Lock validator ported to -rt: it now checks all the sleeping lock
>   variants in -rt too. This helps us catch not only deadlocks but also
>   raw-lock candidates, sooner than before.
>
> - The latest High Resolution Timers queue from Thomas Gleixner with
>   initial support for ARM and PPC. (Kevin Hilman, Deepak Saksena,
>   Sergei Shtylyov)
>
> - The latest GTOD (Generic Time Of Day) queue from John Stultz,
>   including NTP cleanups from Roman Zippel.
>
> - The latest genirq queue: more irq-chip-ization of i686 and x86_64,
>   MSI cleanups from Eric W. Biederman et al.
>
> - The latest preemptible-RCU queue from Paul E McKenney and Dipankar
>   Sarma.
>
> - (assorted fixes and improvements.)
>
>Right now i686 and x86_64 are boot-tested, and ARM is compile-tested.
>The other architectures likely wont even build yet. This being the first
>2.6.18 based release of -rt, some tester caution is called for.
>
>to build a 2.6.18-rt1 tree, the following patches should be applied:
>
>  http://kernel.org/pub/linux/kernel/v2.6/linux-2.6.18.tar.bz2
>  http://redhat.com/~mingo/realtime-preempt/patch-2.6.18-rt1
>
>as usual, bugreports, fixes and suggestions are welcome,
>
> Ingo
>
I hadn't built one of these in quite a while, mainly because I could never 
get tvtime to run while booted to them, some sort of a dma related failure 
I think, so I rather dropped off the path here.

But the announcement was enough to make me try to build it, sort of the 
ultimate "can an old fart build it test", but the make exits with:

  LD      .tmp_vmlinux1
kernel/built-in.o(.text+0x16f25): In function `hrtimer_start':
: undefined reference to `hrtimer_update_timer_prio'
make: *** [.tmp_vmlinux1] Error 1

about half way thru the normal time.  config attached.  I don't think hires 
timers are enabled.

Comments?

-- 
Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
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message by Gene Heskett are:
Copyright 2006 by Maurice Eugene Heskett, all rights reserved.

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