Re: Typo in ULE in FreeBSD 8.0 -- that's not really a bug
On Mon, 10 Nov 2008, Murty, Ravi wrote:
> Hello All,
> I have been playing with ULE in 8.0 and while staring at tdq_notify noticed an interesting (and what seems like a typo) problem.
> The intention of the function is obvious, send an IPI to notify the remote CPU of some new piece of work. In the case where there is no IPI currently pending on the target CPU and this thread should be preempting what's running there, the code checks in td (passed in as a parameter) is the IDLE thread (TDF_IDLETD). If so, it checks the state and sees if idle is RUNNING and if so figures it will notice this new work and we don't really need to send an expensive IPI. However, why would td (parameter) ever be the IDLE thread? It almost seems like this check will always fail and we end up sending a hard IPI to the target CPU which works, but may not be needed. May be we wanted to use PCPU->curthread instead of td?[/color]
Wow ravi, thanks. That's what it was at one point. It must've been
refactored into brokenness. I'll fix and test soon. This has probably
reduced the effectiveness of the mwait patch.
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