Re: [Lse-tech] lockmeter problems.....

[Theodore Ts'o <ty...@mi...>]

On Sun, Jul 27, 2003 at 12:21:35PM -0500, Ray Bryant wrote:
> Hanna,
> 
> David Hansen mentioned something at the OLS performance tools bof about 
> there being a problem with lockmeter (sometimes lock hold times are 
> being reported that are wildly out of whack).  Are you aware of such a 
> problem (this was in 2.6-test).
> 
> If so, I'd appreciate being pointed at a test case and I will see what I 
> can do about this.

Well, there was a problem I discovered where some of the newer
spinlock primitives weren't getting instrumented, and so code
sequences of the form:

	while (queue_not_empty)
			...
		spin_lock_irq()
			...
		spin_unlock()
			...
		spin_lock()
			...
		spin_unlock_irqresture()
			...
		do something that takes a long, long time....
	}

where the *_irq, *_irqreqstore functions were not being instrumented.

I believe Hanna fixed this, but I don't know how well the fix was
propagated; maybe some folks were using an unfixed version, perhaps?

Another possibility is that some other spinlock variant is still not
being instrumented and Hanna and I both missed it.  I'd certainly
start by auditing spinlock.h after applying the lockmeter patch as an
initial starting point.

							- Ted