Messages in this thread | | | Date | Thu, 16 Feb 2006 21:04:43 +0100 (MET) | From | Esben Nielsen <> | Subject | Re: [patch 0/6] lightweight robust futexes: -V3 - Why in userspace? |
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On Thu, 16 Feb 2006, Arjan van de Ven wrote:
> On Thu, 2006-02-16 at 20:06 +0100, Esben Nielsen wrote: > > I just jump into a thread somewhere to ask my question :-) > > > > Why does the list have to be in userspace? > > because it's faster ;) > > Faster??? As I see it, extra manipulations have to be done even in the non-congested case: Every time the lock is taken the locking thread has to add the lock to a the list, and reversely remove the lock from the list. I.e. instructions are _added_ to the fast path where you stay purely in userspace.
I am ofcourse comparing to a solution where you do a syscall on everytime you do a lock. What I am asking about is whethere it wouldn't be enough to maintain the list at the FUTEX_WAIT/FUTEX_WAKE operation - i.e. the slow path where you have to go into the kernel.
Esben
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