On Sunday, January 9, 2011, ron minnich <rminn...@gmail.com> wrote: > On Sun, Jan 9, 2011 at 1:38 PM, Bakul Shah <bakul+pl...@bitblocks.com> wrote: > >> I didn't say plan9 "suffers". Merely that one has to look at >> other aspects as well (implying putting in Tstream may not >> make a huge difference). > > well, what we do know from one set of measurements is that it makes a > measurable difference when latency is measured in the tens of > milliseconds. :-) > > I have done some of these other measurements, e.g. system call > overhead. Plan 9 system call time is quite a bit longer than Linux > nowadays, when Linux uses the SYSENTER support.
Linux maps the kernel in the high 1GB of VM too doesn't it? What does Plan 9 do (haven't looked yet) > > At the same time, the Plan 9 "mon" device that Andrey wrote was > considerably faster than the procfs-based "mon" device I wrote: 30K > samples/second on Plan 9 vs. 12K samples/second on Linux. > > John did do some measurement of file system times via the trace device > we wrote. I think it's fair to say that the IO path for fossil is > considerably slower than the IO path for kernel-based file systems in > Linux: slower as in multiples of 10, not multiples. There's a fair > amount of copying, allocation, and bouncing in and out of the kernel, > and this activity does not come cheap. > > So, one speculation is that a kernel-based Plan 9 file system might be > quite fast. And that's enough random text for a Sunday. Well number of syscalls to hand off delegating filesystem tasks to a userspace filesystem implementation is key. Microkernels try to optimize this as do virtualization hypervisors, because, as observed, bouncing around between kernel and userspace gives performance hopes the beat-down. > > ron > >
