I'm sure it isn't *that* bad for average workloads. Sure, if you hammer
the TTY layer madly to measure the BKL it will show up, but that isn't
an average workload.
I purposely didn't mention this in the previous mail. The tty code is
beyond any type of "peeling". The whole thing relies on the behaviour
of the BKL - in that when you sleep the BKL is released. Think about
someone opening /dev/cua0 while /dev/ttyS0 is trying to be opened, or
a hangup while a port is being opened, or... the list is endless.
It's not as simple as replacing the BKL with a semaphore or spinlock.
I've actually brought this up in passing with Alan back in October - his
feeling at the time was (iirc) that the effort required isn't worth the
rewards you'd get.
When I talked to Ted last, Ted was going to rewrite the whole thing to
get it into a reasonable shape, which included a BKL free tty layer.
I've not heard anything from Ted recently on this though.
However, being able to type on a laptop over a ssh connection to another
machine, and have everything freeze while the hard disk spins up for no
apparant reason (other than your typing) is an annoyance that I wouldn't
mind see "disappear".
-- Russell King (email@example.com) The developer of ARM Linux http://www.arm.linux.org.uk/personal/aboutme.html
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