On Tue, Feb 28, 2023 at 1:40 AM Zhuo, Qiuxu <qiuxu.zhuo@xxxxxxxxx> wrote: > [...] > > > If so, we might make rcupdate.boot_end_delay = 0 as the default value > > > (NOT the default 20s) for CONFIG_PREEMPT_RT=y kernels? > > > > Could you measure how much time your RT system takes to boot before the > > application runs? > > I don't have a real-time OS environment to measure the OS boot time. > I tried to measure the OS boot time of my "CentOS Stream 8" w/o and > w/ Joel’s patch. > > My testing showed the positive result that the OS boot time was > reduced by ~4.6% on my side after applying Joel’s patch. Wow, this is great! I am guessing you have CONFIG_RCU_LAZY disabled, when you tested. If so, that is great news that expediting RCU for a bit longer improves boot time! Please confirm that your config had LAZY disabled. > For testing details, please see the below: > > 1) Testing environment: > OS : CentOS Stream 8 (non-RT OS) > Kernel : v6.2 > Machine : Intel Cascade Lake server (2 sockets, each with 44 logical threads) > Qemu args : -cpu host -enable-kvm, -smp 88,threads=2,sockets=2, … > > 2) My OS boot time definition: > The time from the start of the kernel boot to the shell command line > prompt is shown from the console. [ Different people may have > different OS boot time definitions. ] > > 3) My measurement method (very rough method): > A timer in the kernel periodically prints the boot time every 100ms. > As soon as the shell command line prompt is shown from the console, > we record the boot time printed by the timer, then the printed boot > time is the OS boot time. Hmm, Can you not just print the boot time from userspace using clock_gettime() and CLOCK_BOOTTIME? But yeah either way, good data! > The console log (mixed userspace and kernel logs) looked like this: > > [ OK ] Started Permit User Sessions. > Starting Terminate Plymouth Boot Screen... > Starting Hold until boot process finishes up... > [ OK ] Started Command Scheduler. > [ 6.824466] input: ImExPS/2 Generic Explorer ... > [ 6.884685] Boot ms 6863 > ... > [ 7.170920] Spectre V2 : WARNING: Unprivileged eBPF ... > [ 7.173140] Spectre V2 : WARNING: Unprivileged eBPF ... > [ 7.196741] Boot ms 7175 > ... > [ 8.236757] Boot ms 8215 > > CentOS Stream 8 > Kernel 6.2.0-rcu+ on an x86_64 > > login: [ 8.340751] Boot ms 8319 > [ 8.444756] Boot ms 8423 > ... > > Then the log "login: [ 8.340751] Boot ms 8319" roughly showed the OS boot time was ~8.3s. > > 4) Measured OS boot time (in seconds) > a) Measured 10 times w/o Joel's patch: > 8.7s, 8.4s, 8.6s, 8.2s, 9.0s, 8.7s, 8.8s, 9.3s, 8.8s, 8.3s > The average OS boot time was: ~8.7s > > b) Measure 10 times w/ Joel's patch: > 8.5s, 8.2s, 7.6s, 8.2s, 8.7s, 8.2s, 7.8s, 8.2s, 9.3s, 8.4s > The average OS boot time was: ~8.3s. > > The OS boot time was reduced by : 8.7 – 8.3 = 0.4 second > The reduction percentage was : 0.4/8.7 * 100% = 4.6% > > If the testing above makes sense to you, please feel free to > add > > Tested-by: Qiuxu Zhuo <qiuxu.zhuo@xxxxxxxxx> Yes, it makes sense. I will add these. Thanks! - Joel > > Thanks! > -Qiuxu > > > I can change it to default 0 essentially NOOPing it, but I would rather have a > > saner default (10 seconds even), than having someone forget to tune this for > > their system. > > > > Thanks, > > > > - Joel >
