On 21 March 2015 at 08:52, John Baldwin <j...@freebsd.org> wrote: > On 3/20/15 8:46 PM, Mike Tancsa wrote: >> On 3/20/2015 8:15 PM, Konstantin Belousov wrote: >>>> >>>> For the purpose of devfs, does it make sense to bump timestamps like >>>> normal filesystems for each read/write operation? Looks like Mac OS X >>>> will bump timestamps for each operation but Debian don't. >>> >>> First question is, what timecounter hardware is used. I would accept >>> some slowdown from hardware like HPET, but it is indeed surprising >>> if caused by TSC. >>> >>> >> >> David Wolfskill suggested trying the problem commit with >> >> vfs.timestamp_precision=0 >> >> and it does indeed restore performance to what it was. The raw dtrace >> files are available and FlameGraphs can all be found at >> >> http://tancsa.com/time/ > > Do you know why you are using the HPET instead of TSC for timestamping? > Using the TSC can make a non-trivial performance difference since userland > can calculate timestamps without using system calls when it is used. > (That is not related to this case, but switching to the TSC in general is > preferable.) > > There are a few generations of Intel CPUs where you can't mix deeper sleep > states with the TSC as timecounter, but those CPUs are getting to be a bit > older at this point.
What about various VMs? -adrian _______________________________________________ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to "freebsd-stable-unsubscr...@freebsd.org"
