I have an update on netperf-cstate-small-cross-socket results. Reported performance degradation of 2.5% for the UDP stream throughput and 0.6% for the TCP throughput is for message size of 16kB. For smaller message sizes, the performance drop is higher - up to 5% for UDP throughput for a message size of 64B. See the numbers below [1]
We still think that it's acceptable given the gains in other situations (this is again compared to 5.7 vanilla) : * solved the performance drop upto 20% with single instance SPECjbb2005 benchmark on 8 NUMA node servers (particularly on AMD EPYC Rome systems) => this performance drop was INCREASING with higher threads counts (10% for 16 threads and 20 % for 32 threads) * solved the performance drop upto 50% for low load scenarios (SPECjvm2008 and NAS) [1] Hillf's patch compared to 5.7 (rc4) vanilla: TCP throughput Message size (B) 64 -2.6% 128 -2.3% 256 -2.6% 1024 -2.7% 2048 -2.2% 3312 -2.4% 4096 -1.1% 8192 -0.4% 16384 -0.6% UDP throughput 64 -5.0% 128 -3.0% 256 -3.0% 1024 -3.1% 2048 -3.3% 3312 -3.5% 4096 -4.0% 8192 -3.3% 16384 -2.6% On Wed, May 20, 2020 at 3:58 PM Jirka Hladky <jhla...@redhat.com> wrote: > > Hi Hillf, Mel and all, > > thanks for the patch! It has produced really GOOD results. > > 1) It has fixed performance problems with 5.7 vanilla kernel for > single-tenant workload and low system load scenarios, without > performance degradation for the multi-tenant tasks. It's producing the > same results as the previous proof-of-concept patch where > adjust_numa_imbalance function was modified to be a no-op (returning > the same value of imbalance as it gets on the input). > > 2) We have also added Mel's netperf-cstate-small-cross-socket test to > our test battery: > https://github.com/gormanm/mmtests/blob/master/configs/config-network-netperf-cstate-small-cross-socket > > Mel told me that he had seen significant performance improvements with > 5.7 over 5.6 for the netperf-cstate-small-cross-socket scenario. > > Out of 6 different patches we have tested, your patch has performed > the best for this scenario. Compared to vanilla, we see minimal > performance degradation of 2.5% for the udp stream throughput and 0.6% > for the tcp throughput. The testing was done on a dual-socket system > with Gold 6132 CPU. > > @Mel - could you please test Hillf's patch with your full testing > suite? So far, it looks very promising, but I would like to check the > patch thoroughly to make sure it does not hurt performance in other > areas. > > Thanks a lot! > Jirka > > > > > > > > > > > > > On Tue, May 19, 2020 at 6:32 AM Hillf Danton <hdan...@sina.com> wrote: > > > > > > Hi Jirka > > > > On Mon, 18 May 2020 16:52:52 +0200 Jirka Hladky wrote: > > > > > > We have compared it against kernel with adjust_numa_imbalance disabled > > > [1], and both kernels perform at the same level for the single-tenant > > > jobs, but the proposed patch is bad for the multitenancy mode. The > > > kernel with adjust_numa_imbalance disabled is a clear winner here. > > > > Double thanks to you for the tests! > > > > > We would be very interested in what others think about disabling > > > adjust_numa_imbalance function. The patch is bellow. It would be great > > > > A minute... > > > > > to collect performance results for different scenarios to make sure > > > the results are objective. > > > > I don't have another test case but a diff trying to confine the tool > > in question back to the hard-coded 2's field. > > > > It's used in the first hunk below to detect imbalance before migrating > > a task, and a small churn of code is added at another call site when > > balancing idle CPUs. > > > > Thanks > > Hillf > > > > --- a/kernel/sched/fair.c > > +++ b/kernel/sched/fair.c > > @@ -1916,20 +1916,26 @@ static void task_numa_find_cpu(struct ta > > * imbalance that would be overruled by the load balancer. > > */ > > if (env->dst_stats.node_type == node_has_spare) { > > - unsigned int imbalance; > > - int src_running, dst_running; > > + unsigned int imbalance = 2; > > > > - /* > > - * Would movement cause an imbalance? Note that if src has > > - * more running tasks that the imbalance is ignored as the > > - * move improves the imbalance from the perspective of the > > - * CPU load balancer. > > - * */ > > - src_running = env->src_stats.nr_running - 1; > > - dst_running = env->dst_stats.nr_running + 1; > > - imbalance = max(0, dst_running - src_running); > > - imbalance = adjust_numa_imbalance(imbalance, src_running); > > + //No imbalance computed without spare capacity > > + if (env->dst_stats.node_type != env->src_stats.node_type) > > + goto check_imb; > > + > > + imbalance = adjust_numa_imbalance(imbalance, > > + env->src_stats.nr_running); > > + > > + //Do nothing without imbalance > > + if (!imbalance) { > > + imbalance = 2; > > + goto check_imb; > > + } > > + > > + //Migrate task if it's likely to grow balance > > + if (env->dst_stats.nr_running + 1 < > > env->src_stats.nr_running) > > + imbalance = 0; > > > > +check_imb: > > /* Use idle CPU if there is no imbalance */ > > if (!imbalance) { > > maymove = true; > > @@ -9011,12 +9017,13 @@ static inline void calculate_imbalance(s > > env->migration_type = migrate_task; > > env->imbalance = max_t(long, 0, (local->idle_cpus - > > busiest->idle_cpus) >> 1); > > - } > > > > - /* Consider allowing a small imbalance between NUMA groups > > */ > > - if (env->sd->flags & SD_NUMA) > > - env->imbalance = > > adjust_numa_imbalance(env->imbalance, > > - busiest->sum_nr_running); > > + /* Consider allowing a small imbalance between NUMA > > groups */ > > + if (env->sd->flags & SD_NUMA && > > + local->group_type == busiest->group_type) > > + env->imbalance = > > adjust_numa_imbalance(env->imbalance, > > + > > busiest->sum_nr_running); > > + } > > > > return; > > } > > -- > > > > > -- > -Jirka -- -Jirka
