Messages in this thread | | | Date | Fri, 28 Jan 2005 17:16:45 +0100 | From | Ingo Molnar <> | Subject | Re: Real-time rw-locks (Re: [patch] Real-Time Preemption, -RT-2.6.10-rc2-mm3-V0.7.32-15) |
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* William Lee Irwin III <wli@holomorphy.com> wrote:
> The performance relative to mutual exclusion is quantifiable and very > reproducible. [...]
yes, i dont doubt the results - my point is that it's not proven that the other, more read-friendly types of locking underperform rwlocks. Obviously spinlocks and rwlocks have the same cache-bounce properties, so rwlocks can outperform spinlocks if the read path overhead is higher than that of a bounce, and reads are dominant. But it's still a poor form of scalability. In fact, when the read path is really expensive (larger than say 10-20 usecs) an rwlock can produce the appearance of linear scalability, when compared to spinlocks.
> As far as performance relative to RCU goes, I suspect cases where > write-side latency is important will arise for these. Other lockless > methods are probably more appropriate, and are more likely to dominate > rwlocks as expected. For instance, a reimplementation of the radix > trees for lockless insertion and traversal (c.f. lockless pagetable > patches for examples of how that's carried out) is plausible, where > RCU memory overhead in struct page is not.
yeah.
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