Re: [PATCH 6/7] mm: parallelize deferred_init_memmap()

From: Alexander Duyck
Date: Tue May 05 2020 - 10:55:57 EST

On Mon, May 4, 2020 at 7:11 PM Daniel Jordan <daniel.m.jordan@xxxxxxxxxx> wrote:
>
> On Mon, May 04, 2020 at 09:48:44PM -0400, Daniel Jordan wrote:
> > On Mon, May 04, 2020 at 05:40:19PM -0700, Alexander Duyck wrote:
> > > On Mon, May 4, 2020 at 4:44 PM Josh Triplett <josh@xxxxxxxxxxxxxxxx> wrote:
> > > >
> > > > On May 4, 2020 3:33:58 PM PDT, Alexander Duyck <alexander.duyck@xxxxxxxxx> wrote:
> > > > >On Thu, Apr 30, 2020 at 1:12 PM Daniel Jordan
> > > > ><daniel.m.jordan@xxxxxxxxxx> wrote:
> > > > >> /*
> > > > >> - * Initialize and free pages in MAX_ORDER sized increments so
> > > > >> - * that we can avoid introducing any issues with the buddy
> > > > >> - * allocator.
> > > > >> + * More CPUs always led to greater speedups on tested
> > > > >systems, up to
> > > > >> + * all the nodes' CPUs. Use all since the system is
> > > > >otherwise idle now.
> > > > >> */
> > > > >
> > > > >I would be curious about your data. That isn't what I have seen in the
> > > > >past. Typically only up to about 8 or 10 CPUs gives you any benefit,
> > > > >beyond that I was usually cache/memory bandwidth bound.
> >
> > On Skylake it took more than 8 or 10 CPUs, though on other machines the benefit
> > of using all versus half or 3/4 of the CPUs is less significant.
> >
> > Given that the rest of the system is idle at this point, my main concern is
> > whether other archs regress past a certain thread count.
>
> Reposting the data to be consistent with the way the percentages are reported
> in the changelog.
>
>
> Intel(R) Xeon(R) Platinum 8167M CPU @ 2.00GHz (Skylake, bare metal)
> 2 nodes * 26 cores * 2 threads = 104 CPUs
> 384G/node = 768G memory
>
> kernel boot deferred init
> ------------------------ ------------------------
> node% (thr) speedup time_ms (stdev) speedup time_ms (stdev)
> ( 0) -- 4056.7 ( 5.5) -- 1763.3 ( 4.2)
> 2% ( 1) -2.4% 4153.3 ( 2.5) -5.6% 1861.7 ( 5.5)
> 12% ( 6) 35.0% 2637.7 ( 38.7) 80.3% 346.7 ( 37.5)
> 25% ( 13) 38.4% 2497.3 ( 38.5) 88.1% 210.0 ( 41.8)
> 37% ( 19) 38.9% 2477.0 ( 19.0) 89.5% 185.3 ( 21.5)
> 50% ( 26) 39.1% 2471.7 ( 21.4) 89.8% 179.7 ( 25.8)
> 75% ( 39) 39.5% 2455.7 ( 33.2) 90.8% 161.7 ( 29.3)
> 100% ( 52) 39.9% 2436.7 ( 2.1) 91.8% 144.3 ( 5.9)
>
>
> Intel(R) Xeon(R) CPU E5-2699C v4 @ 2.20GHz (Broadwell, bare metal)
> 1 node * 16 cores * 2 threads = 32 CPUs
> 192G/node = 192G memory
>
> kernel boot deferred init
> ------------------------ ------------------------
> node% (thr) speedup time_ms (stdev) speedup time_ms (stdev)
> ( 0) -- 1957.3 ( 14.0) -- 1093.7 ( 12.9)
> 3% ( 1) 1.4% 1930.7 ( 10.0) 3.7% 1053.3 ( 7.6)
> 12% ( 4) 41.2% 1151.7 ( 9.0) 74.5% 278.7 ( 0.6)
> 25% ( 8) 46.3% 1051.0 ( 7.8) 83.7% 178.0 ( 2.6)
> 38% ( 12) 48.7% 1003.3 ( 7.6) 87.0% 141.7 ( 3.8)
> 50% ( 16) 48.2% 1014.3 ( 20.0) 87.8% 133.3 ( 3.2)
> 75% ( 24) 49.5% 989.3 ( 6.7) 88.4% 126.3 ( 1.5)
> 100% ( 32) 49.1% 996.0 ( 7.2) 88.4% 127.3 ( 5.1)
>
>
> Intel(R) Xeon(R) CPU E5-2699 v3 @ 2.30GHz (Haswell, bare metal)
> 2 nodes * 18 cores * 2 threads = 72 CPUs
> 128G/node = 256G memory
>
> kernel boot deferred init
> ------------------------ ------------------------
> node% (thr) speedup time_ms (stdev) speedup time_ms (stdev)
> ( 0) -- 1666.0 ( 3.5) -- 618.0 ( 3.5)
> 3% ( 1) 1.0% 1649.7 ( 1.5) 2.9% 600.0 ( 1.0)
> 11% ( 4) 25.9% 1234.7 ( 21.4) 70.4% 183.0 ( 22.5)
> 25% ( 9) 29.6% 1173.0 ( 10.0) 80.7% 119.3 ( 9.6)
> 36% ( 13) 30.8% 1153.7 ( 17.0) 84.0% 99.0 ( 15.6)
> 50% ( 18) 31.0% 1150.3 ( 15.5) 84.3% 97.3 ( 16.2)
> 75% ( 27) 31.0% 1150.3 ( 2.5) 84.6% 95.0 ( 5.6)
> 100% ( 36) 31.3% 1145.3 ( 1.5) 85.6% 89.0 ( 1.7)
>
>
> AMD EPYC 7551 32-Core Processor (Zen, kvm guest)
> 1 node * 8 cores * 2 threads = 16 CPUs
> 64G/node = 64G memory
>
> kernel boot deferred init
> ------------------------ ------------------------
> node% (thr) speedup time_ms (stdev) speedup time_ms (stdev)
> ( 0) -- 1029.7 ( 42.3) -- 253.7 ( 3.1)
> 6% ( 1) 3.3% 995.3 ( 21.4) 4.3% 242.7 ( 5.5)
> 12% ( 2) 14.0% 885.7 ( 24.4) 46.4% 136.0 ( 5.2)
> 25% ( 4) 18.9% 835.0 ( 21.5) 66.1% 86.0 ( 1.7)
> 38% ( 6) 21.9% 804.7 ( 15.7) 71.4% 72.7 ( 2.1)
> 50% ( 8) 20.8% 815.3 ( 11.7) 74.4% 65.0 ( 3.5)
> 75% ( 12) 23.5% 787.7 ( 2.1) 74.0% 66.0 ( 3.6)
> 100% ( 16) 23.3% 789.3 ( 15.0) 76.3% 60.0 ( 5.6)
>
>
> AMD EPYC 7551 32-Core Processor (Zen, kvm guest)
> 1 node * 2 cores * 2 threads = 4 CPUs
> 16G/node = 16G memory
>
> kernel boot deferred init
> ------------------------ ------------------------
> node% (thr) speedup time_ms (stdev) speedup time_ms (stdev)
> ( 0) -- 757.7 ( 17.1) -- 57.0 ( 0.0)
> 25% ( 1) -1.0% 765.3 ( 5.5) 3.5% 55.0 ( 0.0)
> 50% ( 2) 4.7% 722.3 ( 21.5) 42.7% 32.7 ( 4.6)
> 75% ( 3) 3.7% 729.7 ( 4.9) 54.4% 26.0 ( 0.0)
> 100% ( 4) 6.2% 710.3 ( 15.0) 63.2% 21.0 ( 0.0)
>
>
> Intel(R) Xeon(R) CPU E5-2699 v3 @ 2.30GHz (Haswell, kvm guest)
> 1 node * 2 cores * 2 threads = 4 CPUs
> 14G/node = 14G memory
>
> kernel boot deferred init
> ------------------------ ------------------------
> node% (thr) speedup time_ms (stdev) speedup time_ms (stdev)
> ( 0) -- 656.3 ( 7.1) -- 57.3 ( 1.5)
> 25% ( 1) 1.8% 644.7 ( 3.1) 0.6% 57.0 ( 0.0)
> 50% ( 2) 6.5% 613.7 ( 5.1) 40.7% 34.0 ( 5.3)
> 75% ( 3) 6.9% 611.3 ( 6.7) 57.6% 24.3 ( 0.6)
> 100% ( 4) 8.6% 599.7 ( 5.9) 62.8% 21.3 ( 1.2)

One question about this data. What is the power management
configuration on the systems when you are running these tests? I'm
just curious if CPU frequency scaling, C states, and turbo are
enabled? I ask because that is what I have seen usually make the
difference in these kind of workloads as the throughput starts
dropping off as you start seeing the core frequency lower and more
cores become active.