On Wed, Jun 10, 2009 at 12:08:43AM -0700, Kip Macy wrote: > On Wed, Jun 10, 2009 at 12:00 AM, Dmitry Morozovsky<ma...@rinet.ru> wrote: > > On Tue, 9 Jun 2009, Kip Macy wrote: > > > > KM> > KM> As far as I can tell systems that have less than 4GB are more > > often hurt > > KM> > KM> by prefetched than helped. On i386 systems and systems with > > less than 4GB, > > KM> > KM> prefetch is now disabled by default. I've added a prefetch > > enable tunable, to > > KM> > KM> enable prefetching for those systems. The prefetch disable > > tunable will continue > > KM> > KM> to unconditionally disable prefetching. > > KM> > KM> > > KM> > > > KM> > [snip] > > KM> > > > KM> > KM> +extern int zfs_prefetch_disable; > > KM> > KM> +extern int zfs_prefetch_enable; > > KM> > > > KM> > [snip] > > KM> > > > KM> > Before the interface is not settled in stone, don't you think simple > > bool > > KM> > zfs_prefetch tunable (defauled to what looks more reasonable to > > partucilar > > KM> > arch/memsize) is more clean and straightforward? > > KM> > > > KM> > > KM> Yes. But the semantics I want don't lend themselves well to a boolean. > > KM> I want it to default to off for i386 and amd64 w/ < 4GB and on for > > KM> amd64 > 4GB. However, I want it to be possible for users with larger > > KM> memory systems to disable it and users with smaller memory systems to > > KM> enable it. The only way a simple boolean would work would be if it > > KM> were zfs_prefetch_non_default_behavior, which I think is even more > > KM> confusing than what I have now. > > > > Hmm, I failed to see how boolean prevent the usage: > > > > if arch==i386 || memsize < 4G > > zfs_prefetch=0 > > else > > zfs_prefetch=1 > > > > and admin can flip the switch to non-default position. > > > > Right, what you're advocating is zfs_prefetch_non_default. Which is > simpler, but still rather weird.
Having special zfs_prefetch_non_default tunable implies that zfs_prefetch can be only set once (i.e. at boot time), and cannot be flipped later. Is that true? If not, I fail to see the need for zfs_prefetch_non_default or original two-sysctl implementation. ./danfe _______________________________________________ svn-src-all@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
