On Sat, May 22, 2021 at 01:12:23PM -0700, Mark Millard via freebsd-arm wrote: >of "cold" cache). Another form of "cold" cache could >result from changing compiler options that would change >the code generated for (nearly) every file produced so >that the cache becomes ineffective. > >"hot" refers to having a significant amount of >"effective/used cache content" that makes a notable >difference in the build times. I'm not that impressed >with the terminology but it is was I've seen used the >most frequently for ccache. So I used it. OK >I'm confused how you can know it "provides tremendous >speedups" while simultaneously not knowing "when ccache >was last used for building anything". what I meant was "I'm not sure of the last time I built anything that used ccache" or, more accurately, "I can't remember the last time I built anything on that machine" because some building uses ccache, others not. But I know that buildworld and friends use ccache. >Remember that when comparing to my "from scratch" >build times: in my build everything was compiled >and linked, no prior build materials around to be >reused. So I'm reporting a context where I know >how to interpret the result and I'm presenting >enough history to establish a repeatable context. OK I ran another build. Same sources. 1. rm -rf /usr/obj && mkdir /usr/obj 2. rm -rf /var/cache/ccache && mkdir /var/cache/ccache then: make -j10 cleanworld started on Sat May 22 19:10:02 BST 2021 make -j10 cleanworld completed on Sat May 22 19:10:02 BST 2021 # make -j10 cleandir started on Sat May 22 19:10:02 BST 2021 make -j10 cleandir completed on Sat May 22 19:10:37 BST 2021 # make -j10 clean started on Sat May 22 19:10:37 BST 2021 make -j10 clean completed on Sat May 22 19:10:58 BST 2021 # make -j6 buildworld started on Sat May 22 19:10:58 BST 2021 make -j6 buildworld completed on Sun May 23 00:47:03 BST 2021 # make -j6 buildkernel started on Sun May 23 00:47:03 BST 2021 make -j6 buildkernel completed on Sun May 23 01:20:31 BST 2021 so buildworld took 5hr 36min 5s and buildkernel 33min 28s from cold. earlier, I wrote: >> make -j6 buildworld started on Sat May 22 15:44:11 BST 2021 >> make -j6 buildworld completed on Sat May 22 16:20:48 BST 2021 >> make -j6 buildkernel started on Sat May 22 16:20:48 BST 2021 >> make -j6 buildkernel completed on Sat May 22 16:49:18 BST 2021 36min 37s for make buildworld and 28min 30s for make buildkernel. This is what I meant by "tremendous speedups". Other things get built on this machine; it has a poudriere instance. So I guess anything using C or C++ will use the ccache when building. I might not know exactly *when* unless I also know (when whatever the machine was compiling), it used something that ccache could be used for. -- J.
Original text of this message