2.2.19pre3 and poor reponse to RT-scheduled processes?

[Rafal Boni <rafal.boni@eDial.com>]

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[...Please CC me on any replies, as I'm not on the list(s)...]

Folks:
	I was experiencing problems with 2.2.16 where the box would go out
	to lunch for a few seconds flushing buffer or paging at inopportune
	times (is there ever an opportune time for the box to become non-
	reponsive for 5 seconds? 8-).

	2.2.19pre3 makes the behaviour much better, but I still see ~ 2sec
	pauses at times.  I'm sending this to the MM list as well, since I
	believe the poor behaviour in 2.2.16 was an MM issue... I don't 
	know where the slowdowns are happening this time around.

	The box in question is running the linux-ha.org heartbeat package,
	which is a RT-scheduled, mlock()'ed process, and as such should
	get as good service as the box is able to mange.  Often, under
	high disk (and/or MM) loads, the box becomes unreponsive for a
	period of time from ~ 1 sec to a high of ~ 2.8sec.

	The test is simply running a 'dd if=/dev/zero of=/u1/big-empty-file
	bs=1k count=512000 && date'.  Generally, the box will sieze up around
	the same time as the the 'dd' finishes (maybe trying to exec date?).

	I'd appreciate any hints at how to reduce the non-reponsiveness 
	window down as much as possible.  I haven't yet looked to see if
	there is a version of the low-latency patches for 2.2.18 or 19pre,
	but I'd appreciate other ideas on tracking this down as well.

Thanks!
- --rafal

- ----
Rafal Boni                                               rafal.boni@eDial.com
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    Need to get a hold of me?  http://800.eDial.com/rafal.boni@eDial.com

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