Raghu, thanks for you input. I'm more than glad to work together with you to make this idea work better. -Jiannan On Thu, Jun 6, 2013 at 11:15 PM, Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx> wrote: > On 06/03/2013 11:51 AM, Raghavendra K T wrote: >> >> On 06/03/2013 07:10 AM, Raghavendra K T wrote: >>> >>> On 06/02/2013 09:50 PM, Jiannan Ouyang wrote: >>>> >>>> On Sun, Jun 2, 2013 at 1:07 AM, Gleb Natapov <gleb@xxxxxxxxxx> wrote: >>>> >>>>> High level question here. We have a big hope for "Preemptable Ticket >>>>> Spinlock" patch series by Jiannan Ouyang to solve most, if not all, >>>>> ticketing spinlocks in overcommit scenarios problem without need for >>>>> PV. >>>>> So how this patch series compares with his patches on PLE enabled >>>>> processors? >>>>> >>>> >>>> No experiment results yet. >>>> >>>> An error is reported on a 20 core VM. I'm during an internship >>>> relocation, and will start work on it next week. >>> >>> >>> Preemptable spinlocks' testing update: >>> I hit the same softlockup problem while testing on 32 core machine with >>> 32 guest vcpus that Andrew had reported. >>> >>> After that i started tuning TIMEOUT_UNIT, and when I went till (1<<8), >>> things seemed to be manageable for undercommit cases. >>> But I still see degradation for undercommit w.r.t baseline itself on 32 >>> core machine (after tuning). >>> >>> (37.5% degradation w.r.t base line). >>> I can give the full report after the all tests complete. >>> >>> For over-commit cases, I again started hitting softlockups (and >>> degradation is worse). But as I said in the preemptable thread, the >>> concept of preemptable locks looks promising (though I am still not a >>> fan of embedded TIMEOUT mechanism) >>> >>> Here is my opinion of TODOs for preemptable locks to make it better ( I >>> think I need to paste in the preemptable thread also) >>> >>> 1. Current TIMEOUT UNIT seem to be on higher side and also it does not >>> scale well with large guests and also overcommit. we need to have a >>> sort of adaptive mechanism and better is sort of different TIMEOUT_UNITS >>> for different types of lock too. The hashing mechanism that was used in >>> Rik's spinlock backoff series fits better probably. >>> >>> 2. I do not think TIMEOUT_UNIT itself would work great when we have a >>> big queue (for large guests / overcommits) for lock. >>> one way is to add a PV hook that does yield hypercall immediately for >>> the waiters above some THRESHOLD so that they don't burn the CPU. >>> ( I can do POC to check if that idea works in improving situation >>> at some later point of time) >>> >> >> Preemptable-lock results from my run with 2^8 TIMEOUT: >> >> +-----------+-----------+-----------+------------+-----------+ >> ebizzy (records/sec) higher is better >> +-----------+-----------+-----------+------------+-----------+ >> base stdev patched stdev %improvement >> +-----------+-----------+-----------+------------+-----------+ >> 1x 5574.9000 237.4997 3484.2000 113.4449 -37.50202 >> 2x 2741.5000 561.3090 351.5000 140.5420 -87.17855 >> 3x 2146.2500 216.7718 194.8333 85.0303 -90.92215 >> 4x 1663.0000 141.9235 101.0000 57.7853 -93.92664 >> +-----------+-----------+-----------+------------+-----------+ >> +-----------+-----------+-----------+------------+-----------+ >> dbench (Throughput) higher is better >> +-----------+-----------+-----------+------------+-----------+ >> base stdev patched stdev %improvement >> +-----------+-----------+-----------+------------+-----------+ >> 1x 14111.5600 754.4525 3930.1602 2547.2369 -72.14936 >> 2x 2481.6270 71.2665 181.1816 89.5368 -92.69908 >> 3x 1510.2483 31.8634 104.7243 53.2470 -93.06576 >> 4x 1029.4875 16.9166 72.3738 38.2432 -92.96992 >> +-----------+-----------+-----------+------------+-----------+ >> >> Note we can not trust on overcommit results because of softlock-ups >> > > Hi, I tried > (1) TIMEOUT=(2^7) > > (2) having yield hypercall that uses kvm_vcpu_on_spin() to do directed yield > to other vCPUs. > > Now I do not see any soft-lockup in overcommit cases and results are better > now (except ebizzy 1x). and for dbench I see now it is closer to base and > even improvement in 4x > > > +-----------+-----------+-----------+------------+-----------+ > ebizzy (records/sec) higher is better > +-----------+-----------+-----------+------------+-----------+ > base stdev patched stdev %improvement > +-----------+-----------+-----------+------------+-----------+ > 5574.9000 237.4997 523.7000 1.4181 -90.60611 > 2741.5000 561.3090 597.8000 34.9755 -78.19442 > 2146.2500 216.7718 902.6667 82.4228 -57.94215 > 1663.0000 141.9235 1245.0000 67.2989 -25.13530 > > +-----------+-----------+-----------+------------+-----------+ > +-----------+-----------+-----------+------------+-----------+ > dbench (Throughput) higher is better > +-----------+-----------+-----------+------------+-----------+ > base stdev patched stdev %improvement > +-----------+-----------+-----------+------------+-----------+ > 14111.5600 754.4525 884.9051 24.4723 -93.72922 > 2481.6270 71.2665 2383.5700 333.2435 -3.95132 > 1510.2483 31.8634 1477.7358 50.5126 -2.15279 > 1029.4875 16.9166 1075.9225 13.9911 4.51050 > +-----------+-----------+-----------+------------+-----------+ > > > IMO hash based timeout is worth a try further. > I think little more tuning will get more better results. > > Jiannan, When you start working on this, I can also help > to get best of preemptable lock idea if you wish and share > the patches I tried. > > > -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
