Re: scheduler: IRQs disabled over context switches

[Davide Libenzi]

On Mon, 24 May 2004, Ingo Molnar wrote:

> 
> * Davide Libenzi <davidel@xxxxxxxxxxxxxxx> wrote:
> 
> > We used to do it in 2.4. What changed to make it fragile? The
> > threading (TLS) thing?
> 
> it _should_ work, but in the past we only had trouble from such changes
> (at least in the O(1) tree of scheduling - 2.4 scheduler is OK.). We
> could try the patch below. It certainly boots on SMP x86. But it causes
> a 3.5% slowdown in lat_ctx so i'd not do it unless there are some really
> good reasons.

IMO it is fine, as long as it works with IRQ disabled. There are archs 
where IRQ latencies matters more than lat_ctx times (that BTW are bogus). 
And we already have the infrastructure in place to let the arch to choose 
the way better fits it. Russel reported that a guy trying it (IRQ enabled 
ctx switch) with MIPS was having some problem with it though.


BTW, the unlock_irq should go in prepare not finish.


- Davide

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