Messages in this thread |  | | Date | Thu, 7 Nov 2002 20:29:25 -0800 | | From | William Lee Irwin III <> | | Subject | Re: ps performance sucks (was Re: dcache_rcu [performance results]) |
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On Thu, 2002-11-07 at 22:57, William Lee Irwin III wrote: >> I'm not sure RCU would help this any; I'd be very much afraid of the >> writes being postponed indefinitely or just too long in the presence >> of what's essentially perpetually in-progress read access. Does RCU >> have a guarantee of forward progress for writers?
On Thu, Nov 07, 2002 at 11:17:21PM -0500, Robert Love wrote: > I am not sure I like the idea of RCU for the tasklist_lock. > I do agree 100% with your first point, though - the problem is > ill-behaved readers. I think the writing vs. reading is such that the > rw-lock we have now is fine, we just need to make e.g. /proc play way > way more fair.
This is only feasible for small numbers of cpus. Any compensation provided by algorithmic improvements on the read-side is outweighed by NR_CPUS. Making readers well-behaved only solves half of the issue. Whether the other half is addressible in a 2.6.x time scale is an open question, but a question I'd like to see answered in favor of fixing the livelocks sooner rather than later (esp. as 2.7+ issues are unlikely to be resolved in line with hardware release schedules). I have a strong bias toward code which works everywhere, all the time.
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