> In addition to that and maybe more promising is the possibility to
> map the page cache straight into the users address space and use copy on
> write if the user modifies the read buffer. (this of course works only
> if the readbuffer is aligned on a 4K boundary and the whole page is read
> in)
Ewww.. That basically *is* an mmap(), though, isn't it..
> I also profiled the mmapped code and found no such bottlenecks. The CPU
> was mostly idle. Unfortunately a lock in the kernel serializes a
> significant part of the mmap operation therefore leading to a slower
> overall execution time (see my previous postings).
Well, it's been mentioned a number of times that one of the big goals for
2.3/2.4 is to improve SMP performance by finer locking granularity, so it
wouldn't surprise me if someone's thinking about this issue already. Maybe
sct has already done it :-)
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