Re: RPi3B -j4 vs. -j3 main [so: 14] from-scratch buildworld times for my context; buildkernel too; swap space usage and such
- Reply: Mark Millard : "Re: RPi3B -j4 vs. -j3 main [so: 14] from-scratch buildworld times for my context; buildkernel too; swap space usage and such"
- In reply to: Mark Millard : "RPi3B -j4 vs. -j3 main [so: 14] from-scratch buildworld times for my context; buildkernel too; swap space usage and such"
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Date: Thu, 25 May 2023 01:51:26 UTC
On Wed, May 24, 2023 at 05:46:11PM -0700, Mark Millard wrote: > RPi3B -j4 vs. -j3 buildworld times for my context: > > World built in 120764 seconds, ncpu: 4, make -j4 [So a little under 33 hr 35 min] > World built in 115635 seconds, ncpu: 4, make -j3 [So a little under 32 hr 10 min] > [A delta of a little under 1hr 30min] > > So: -j4 buildworld spent more time waiting for its trashing of > the swap space than time it gained from having use of a 4th > core. The trashing is mostly during building of libllvm, libclang, > and liblldb. The RPi3B RAM subsystem can limit the gain from > having more cores active as well. > > > By contrast . . . > > RPi3B -j4 vs. -j3 buildkernel times for my context: > > Kernel(s) GENERIC-NODBG-CA53 built in 7836 seconds, ncpu: 4, make -j4 [So a little under 2 hr 15 min] > Kernel(s) GENERIC-NODBG-CA53 built in 8723 seconds, ncpu: 4, make -j3 [So a little under 2 hr 30 min] > [A delta of a little under 15 min] > > So: -j4 buildkernel spent less time waiting for its trashing of > the swap space than time it gained from having use of a 4th > core. (Not much thrashing occurred.) > > > And mem/swap usage info for buildworld+buildkernel . . . > > Overall -j4 vs -j3 buildworld buildkernel info for my context: > > -j4 Mem: . . ., 677688Ki MaxObsActive, 249652Ki MaxObsWired, 950032Ki MaxObs(Act+Wir+Lndry) > -j3 Mem: . . ., 683416Ki MaxObsActive, 315140Ki MaxObsWired, 927424Ki MaxObs(Act+Wir+Lndry) > > -j4 Swap: . . ., 1495Mi MaxObsUsed, 2117Mi MaxObs(Act+Lndry+SwapUsed), 2358Mi MaxObs(Act+Wir+Lndry+SwapUsed) > -j3 Swap: . . ., 1178Mi MaxObsUsed, 1811Mi MaxObs(Act+Lndry+SwapUsed), 2049Mi MaxObs(Act+Wir+Lndry+SwapUsed) > > > > FYI for the context: > make[1]: "/usr/main-src/Makefile.inc1" line 326: SYSTEM_COMPILER: Determined that CC=cc matches the source tree. Not bootstrapping a cross-compiler. > make[1]: "/usr/main-src/Makefile.inc1" line 331: SYSTEM_LINKER: Determined that LD=ld matches the source tree. Not bootstrapping a cross-linker. > > > Notes: > > Incremental buildworld's would depend on how much rebuilding of > libllvm, libclang, and liblldb would happen to occur. > > A system with 2 GiBytes of RAM would have far less trashing of > the swap space. A system with 4 GiBytes of RAM would not thrash > the swap space. The closest comparison I could make with 4 > GiBytes of RAM would be the Rock64 doing a from-scratch build. > It is also cortex-a53 based. As I remember, its RAM subsystem > does not limit multiple cores as easily/much. I've no access to > an analogous 2 GiByte context. > Would a DRAM-backed USB "drive" used only for swap help any? I don't think it's practical, but I'm curious in principle. Long ago I think folks actually made hardware consisting of dynamic RAM coupled to a disk interface, probably SCSI, to get around physical RAM limits on older computers. It's kinda silly for a Pi, and expensive. Thanks for writing! bob prohaska > === > Mark Millard > marklmi at yahoo.com > >