The lockless tag is indeed correct, accurate, and helpful in identifying
the characteristics of the algorithm. More of these algorithms, such as
the recent RCU work, will need to be placed into Linux for it to perform
well on multiprocessors.
The K42 MP OS Project
Advanced Operating Systems
Scalable Parallel Systems
IBM T.J. Watson Research Center
Perez-Gonzalez, Inaky writes:
> > From: Karim Yaghmour [mailto:email@example.com]
> > relayfs actually uses 2 mutually-exclusive schemes internally -
> > 'lockless' and 'locking', depending on the availability of a cmpxchg
> > instruction (lockless needs cmpxchg). If the lockless scheme is being
> > used, relay_lock_channel() does no locking or irq disabling of any
> > kind i.e. it's basically a no-op in that case.
> So that means you are using cmpxchg to do the locking. I mean, not the
> "locking" itself, but a similar process to that of locking. I see.
> However, isn't it the almost the same as spinlocking? You are basically
> trying to "allocate" a channel idx with atomic cmpxchg; if it fails, you
> are retrying, spinning on the retry code until successful.
> Not meaning to be an smartass here, but I don't buy the "lockless" tag,
> I would agree it is an optimized-lock scheme [assuming it works better
> than the spinlock case, that I am sure it does because if not you guys
> would have not gone through the process of implementing it], but it is
> not lockless.
>> Don't get me wrong - I don't mean the actual difference is not important;
>> what I mean is not important is me buying the "lockless" tag or not. I
>> actually think that the method you guys use is really sharp.
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