On Saturday 27 October 2007 06:57:14 Matt Mackall wrote:
> Well I expect once you start letting people easily build strings by
> concatenation, you'll very shortly afterwards have people using them
> in loops. And having hidden O(n^2) behavior in there is a little sad,
> even though n will tend to be small and well-bounded. If we can do
> something simple to avoid it, we should.
Hi Matt,
I avoid typing even a single character of optimization until it's
justified. This is partially a reaction against the machoptimization
tendencies of many kernel programmers, but it's mainly a concern at the
kernel's complexity creep.
Meanwhile, of course, I've now spent far too long analyzing this :)
Building a 1000 byte string 1 byte at a time involves 6 reallocs (SLAB) or 10
reallocs (SLUB). Frankly, that's good enough without an explicit alloc
length field (better in some ways).
As to keeping an explicit length vs strlen(): those 1000 calls on my test
machine take 1491ns per call with an explicit length vs 1496ns per call with
strlen(). That's not worth 4 bytes, let alone a single line of code, O(n^2)
or no.
As the nail in the coffin, callers only use ->buf, so are insulated from any
such optimizations if we decided to do them in future.
Hope that helps,
Rusty.
PS. I don't think we should switch this to a simple char ** tho, as
the "struct stringbuf" gives us some type safety and reminds people not to
simply kfree it.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
