Linus Torvalds <torva...@linux-foundation.org> writes: > On Wed, Aug 23, 2017 at 3:36 PM, Kirill A. Shutemov > <kirill.shute...@linux.intel.com> wrote: >> >> Below is test cases that allocates a lot of page tables and measuare >> fork/exit time. (I'm not entirely sure it's the best way to stress the >> codepath.) > > Looks ok to me. Doing a profile (without the RCU freeing, obviously) gives me > > 0.77% a.out [kernel.vmlinux] [k] free_pgd_range > > ▒ > > so it does seem to spend time in the page directory code. > >> Unpatched: average 4.8322s, stddev 0.114s >> Patched: average 4.8362s, stddev 0.111s > > Ok, I vote for avoiding the complexity of two different behaviors, and > just making the page table freeing use RCU unconditionally.
Thanks Linus & Kirill, I actually did a microbenchmark with mmap/munmap too but wasn't able to see any measurable performace difference. > > If actively trying to trigger that code doesn't show a real measurable > difference, I don't think it matters, and the fewer different code > paths we have, the better. I'll send v2 enabling HAVE_RCU_TABLE_FREE on x86 unconditionally, thanks! -- Vitaly _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel