Re: [uml-devel] Re: TLS support - status - need for re-testing

[Jeff Dike <jdike@addtoit.com>]

On Fri, Mar 24, 2006 at 12:43:33PM +0100, Blaisorblade wrote:
> We discussed this time ago, and read the description of the patch:
> 
> # Also, as suggested by Jeff, remove a redundant enabling of SIGVTALRM,
> # comprised in the subsequent local_irq_enable(). I'm just a bit dubious if
> # ordering matters there...

Oops, nevermind.

> Note this pre-dates soft interrupts, however.

Shouldn't matter.

> > global-ldt-sem - We should be using mutexes now, not semaphores
> 
> That's your patch, but below I drop this.

My patch predates mutexes.

But you still use semaphores, and that should be updated.

> > undo-global-ldt-sem - what's so horrible about the global?  it won't
> > be highly contended, so making a single mutex saves memory from every
> > ldt.
> 
> For memory: 500 existing processes (a huge number in practice) * 20 byte (and
> I think a semaphore is smaller) = 10 Kbyte. We waste more for the kernel 
> stack of 1 thread.
> 
> For reason: the compilation problem can be avoided differently (and the 
> subsequent patch also merges duplicated code).
> 
> I didn't like global_ldt_sem because I felt it unclean; if done for memory 
> usage it's another story, but still we need to check this creates no locking 
> problem (almost surely no, but I want to look at the code well).

It's simpler.  A single global lock is simpler than a lock in every 
datastructure.

				Jeff



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