The last topic on Monday was the "five-minute speed talks," where
developers could briefly raise an issue of interest to them.
Linus started things off by talking about 2.7. It seems that he is getting
very few complaints about the 2.6 kernel; just about everybody, it seems,
is quite happy with it. Says Linus: "that's not good." Without a list of
outstanding issues, there is little pressure to start the 2.7 development
series; why bother, if there's nothing to do?
He has another concern as well. Linus believes that working as a
two-person team with Andrew Morton has been highly effective. Nobody was
prepared to disagree with him on that point. When 2.7 starts, Andrew will
stay with 2.6 and that partnership will end - or, at least, change
significantly. Finding somebody to take
Andrew's place will be a tall order, to say the least.
2.7 is a topic which is to be revisited at the end of the Tuesday session.
Matthew Wilcox noted that PCI Express is taking off more quickly than had
been anticipated, and that PCI Express video cards will likely displace AGP
cards in the near future. Linux, thus, needs to get proper PCI Express
support in place quickly. For various reasons, getting this support in
place will require some memory management changes: PCI Express memory
windows require new attributes which can only be set up using the newish
"physical attribute table" (PAT) mechanism.
Paul McKenney claimed that some scalability issues remain in the kernel; he
talked specifically about the dentry cache. Dentry aging is still done
globally, and the relevant locking slows things down. Fixing this issue
will require some significant rewrites, and is thus a 2.7 issue.
Andrew Morton was a bit annoyed, wondering why he had not heard about this
issue until now. It seems that, since nobody expects the problem to be
fixed in 2.6, it hasn't seen much public discussion so far.
Linus discussed the need for a cache for the readdir() VFS
operation. Of all the filesystem operations, only readdir()
remains uncached, and it is a performance problem in some situations - it
hits Samba servers in particular. Part of that problem is the
result of Samba's implementation of case-insensitive lookups, a feature
which is unlikely to ever find its way into the mainline kernel. Some sort
of readdir() caching may be added, instead, but it
will not be trivial; among other things, some directories can be quite
large and thus hard to cache.
Other topics which came up included the early user space/initramfs work
(which, says Linus, "will never happen," but which is apparently being
shipped now by SUSE); the creation of a set of ABI header files for the
kernel (which looks like a high priority for 2.7); whether OSDL should be
doing more testing for the community (the real need, instead, is more
people looking at the tests being done now); and the eternal goal of
rewriting the TTY layer (which works "just well enough" that nobody can
justify taking the time to fix it).
Getting rid of the timer tick may be an idea whose time will come in 2.7.
The current timer interrupt does not provide the resolution needed for some
tasks, but it comes far too often for other applications. Effective power
management, in particular, needs to be able to turn off timer interrupts
when nothing is happening. So, it has been said, "jiffies must die."
Further discussions took place in unstructured "bar BOFs" and will not be
reported on here.
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