On Thu, 10 Apr 2014 09:44:30 -0500 Clark Williams <williams@xxxxxxxxxx> wrote: > I wrote a program named whack_mmap_sem which creates a large (4GB) > buffer, then creates 2 x ncpus threads that are affined across all the > available cpus. These threads then randomly write into the buffer, > which should cause page faults galore. > > I then built the following kernel configs: > > vanilla-3.13.15 - no RT patches applied vanilla-3.*12*.15? > rt-3.12.15 - PREEMPT_RT patchset > rt-3.12.15-fixes - PREEMPT_RT + rwsem fixes > rt-3.12.15-multi - PREEMPT_RT + rwsem fixes + rwsem-multi patch > > My test h/w was a Dell R520 with a 6-core Intel(R) Xeon(R) CPU E5-2430 > 0 @ 2.20GHz (hyperthreaded). So whack_mmap_sem created 24 threads > which all partied in the 4GB address range. > > I ran whack_mmap_sem with the argument -w 100000 which means each > thread does 100k writes to random locations inside the buffer and then > did five runs per each kernel. At the end of the run whack_mmap_sem > prints out the time of the run in microseconds. > > The means of each group of five test runs are: > > vanilla.log: 1210117 > rt.log: 17210953 (14.2 x slower than vanilla) > rt-fixes.log: 10062027 (8.3 x slower than vanilla) > rt-multi.log: 3179582 (2.x x slower than vanilla) > > > As expected, vanilla kicked RT's butt when hammering on the > mmap_sem. But somewhat unexpectedly, your fixups helped quite a bit That doesn't surprise me too much. As I removed the check for the nesting, which also shrunk the size of the rwsem itself (removed the read_depth from the struct). This itself can give a bonus boost. Now the question is, how much will this affect real use case scenarios? -- Steve > and the multi+fixups got RT back into being almost respectable. > -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
