* Mel Gorman <mgorman@xxxxxxx> wrote: > I found that ebizzy regressed between 3.4 and 3.10 while testing on a new > machine. Bisection initially found at least two problems of which the > first was commit 611ae8e3 (x86/tlb: enable tlb flush range support for > x86). The second was related to ACPI cpufreq and so it was disabled for > the purposes of this series. > > The intent of the TLB range flush patch appeared to be to preserve > existing TLB entries which makes sense. The decision on whether to do a > full mm flush or a number of single page flushes depends on the size of the > relevant TLB and the CPU which is presuably taking the cost of a TLB refill. > It is a gamble because the cost of the per-page flushes must be offset by a > reduced TLB miss count. There are no indications what the cost of calling > invlpg are if there are no TLB entries and it's also not taking into > account how many CPUs it may have to execute these single TLB flushes on. > > Ebizzy sees very little benefit as it discards newly allocated memory very > quickly which is why it appeared to regress so badly. While I'm wary of > optimising for such a benchmark, it's commonly tested and the defaults for > Ivybridge may need to be re-examined. > > The following small series restores ebizzy to 3.4-era performance. Is there a > better way of doing this? Bear in mind that I'm testing on a single IvyBridge > machine and there is no guarantee the gain is universal or even relevant. > > kernel build was tested but it's uninteresting as TLB range is unimportant > to it. A page fault benchmark was also tested but it does not hit the same paths > impacted by commit 611ae8e3. > > ebizzy > 3.13.0-rc3 3.4.69 3.13.0-rc3 > vanilla vanilla newdefault-v1 > Mean 1 7353.60 ( 0.00%) 6782.00 ( -7.77%) 7836.20 ( 6.56%) > Mean 2 8120.40 ( 0.00%) 8278.80 ( 1.95%) 9520.60 ( 17.24%) > Mean 3 8087.80 ( 0.00%) 8083.60 ( -0.05%) 9003.80 ( 11.33%) > Mean 4 7919.20 ( 0.00%) 7842.60 ( -0.97%) 8680.60 ( 9.61%) > Mean 5 7310.60 ( 0.00%) 7740.60 ( 5.88%) 8273.20 ( 13.17%) > Mean 6 6798.00 ( 0.00%) 7720.20 ( 13.57%) 8033.20 ( 18.17%) > Mean 7 6759.40 ( 0.00%) 7644.00 ( 13.09%) 7643.80 ( 13.08%) > Mean 8 6501.80 ( 0.00%) 7666.40 ( 17.91%) 6944.40 ( 6.81%) > Mean 12 6606.00 ( 0.00%) 7523.20 ( 13.88%) 7035.80 ( 6.51%) > Mean 16 6655.40 ( 0.00%) 7287.40 ( 9.50%) 7099.20 ( 6.67%) > Mean 20 6703.80 ( 0.00%) 7152.20 ( 6.69%) 7116.60 ( 6.16%) > Mean 24 6705.80 ( 0.00%) 7014.80 ( 4.61%) 7113.60 ( 6.08%) > Mean 28 6706.60 ( 0.00%) 6940.40 ( 3.49%) 7115.20 ( 6.09%) > Mean 32 6727.20 ( 0.00%) 6878.80 ( 2.25%) 7110.80 ( 5.70%) > Stddev 1 42.71 ( 0.00%) 53.16 (-24.46%) 39.80 ( 6.82%) > Stddev 2 250.26 ( 0.00%) 150.57 ( 39.84%) 31.94 ( 87.24%) > Stddev 3 71.67 ( 0.00%) 69.38 ( 3.19%) 84.13 (-17.39%) > Stddev 4 30.25 ( 0.00%) 87.06 (-187.82%) 31.80 ( -5.14%) > Stddev 5 71.18 ( 0.00%) 25.68 ( 63.92%) 125.24 (-75.95%) > Stddev 6 34.22 ( 0.00%) 23.35 ( 31.75%) 124.40 (-263.57%) > Stddev 7 100.59 ( 0.00%) 112.83 (-12.17%) 65.07 ( 35.31%) > Stddev 8 20.26 ( 0.00%) 43.43 (-114.32%) 48.26 (-138.16%) > Stddev 12 19.43 ( 0.00%) 19.73 ( -1.55%) 23.25 (-19.65%) > Stddev 16 14.47 ( 0.00%) 26.42 (-82.54%) 17.71 (-22.40%) > Stddev 20 21.37 ( 0.00%) 15.97 ( 25.27%) 14.87 ( 30.42%) > Stddev 24 12.87 ( 0.00%) 28.12 (-118.44%) 10.46 ( 18.75%) > Stddev 28 13.89 ( 0.00%) 17.97 (-29.36%) 12.22 ( 12.04%) > Stddev 32 18.14 ( 0.00%) 20.37 (-12.31%) 16.40 ( 9.58%) > > 3.13.0-rc3 3.4.69 3.13.0-rc3 > vanilla vanilla newdefault-v1 > User 900.27 995.20 947.33 > System 1583.41 1680.76 1533.17 > Elapsed 2100.78 2100.81 2100.76 > > This shows the ebizzy comparison between 3.13-rc3, 3.4.69-stable and this series. > The series is not a universal win against 3.4 but the figure are generally better > and system CPU usage is reduced. I think you found a real bug and I definitely agree that we want to fix it - the TLB range optimization was supposed to be a (nearly) unconditional win, so a regression like this is totally not acceptable IMHO. Please help me out with interpreting the numbers. The Ebizzy table: > ebizzy > 3.13.0-rc3 3.4.69 3.13.0-rc3 > vanilla vanilla newdefault-v1 > Mean 1 7353.60 ( 0.00%) 6782.00 ( -7.77%) 7836.20 ( 6.56%) > Mean 2 8120.40 ( 0.00%) 8278.80 ( 1.95%) 9520.60 ( 17.24%) > Mean 3 8087.80 ( 0.00%) 8083.60 ( -0.05%) 9003.80 ( 11.33%) is the first numeric column number of threads/clients? The other colums are showing pairs of throughput (higher is better), with a performance regression percentage in parentheses. do the stddev numbers: > Stddev 1 42.71 ( 0.00%) 53.16 (-24.46%) 39.80 ( 6.82%) > Stddev 2 250.26 ( 0.00%) 150.57 ( 39.84%) 31.94 ( 87.24%) ... correspond to the respective thread count and thus overlay the first table, right? stddev appears to be rather large especially around a client count of 7-8. It will be difficult to fine-tune the TLB range flush constants if noise is too large. Regarding total CPU usage: > 3.13.0-rc3 3.4.69 3.13.0-rc3 > vanilla vanilla newdefault-v1 > User 900.27 995.20 947.33 > System 1583.41 1680.76 1533.17 > Elapsed 2100.78 2100.81 2100.76 ... elapsed time appears to be the same - does the benchmark run for a constant amount of time, regardless of performance? This means that higher user time and lower system time generally represents higher achieved throughput, right? Yet the sum does not appear to be constant across kernels - does this mean that even newdefault-v1 is idling around more than v3.4.69? Thanks, Ingo -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>