On Sat, Jun 15, 2013 at 02:31:34PM +0300, Konstantin Belousov wrote: > On Sat, Jun 15, 2013 at 01:26:10PM +0200, Luigi Rizzo wrote: > > With "indirect buffers" in netmap/vale, i can eliminate the A->B copy, > > and do A->C with a copyin in the kernel of the host. > > But the per-packet budget is minuscule, and i am afraid that doing > > an unconditional vslock() on each buffer is going to be too expensive > > (and then i should also unwire the page ? > > Using vslock() causes enormous user map fragmentation and should be > avoided. The cost is basically the same as the page fault, since > vslock() is a wrapper around vm_map_wire(), which just calls page fault > handler for each address in region. > > On the other hand, I do not understand how any kernel-side lock would > prevent usermode from unmapping a buffer while other thread in kernel > mode access it.
the lock i was talking about in previous emails protects the in-kernel data structures (B, C and the VALE switch), which are manipulated within system calls. The user buffer A is not protected, i am happy to take a page fault in the rare case it happens (and normally it won't because in my application A has been written to just moments before). cheers luigi _______________________________________________ freebsd-current@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-current To unsubscribe, send any mail to "freebsd-current-unsubscr...@freebsd.org"
