Hello. (Sorry for necroposting, found this upstream reference only now.)
On Mon, Apr 20, 2020 at 03:04:53PM +0800, Muchun Song
<songmuc...@bytedance.com> wrote:
> /* Time spent by the tasks of the CPU accounting group executing in ... */
> @@ -339,7 +340,7 @@ void cpuacct_charge(struct task_struct *tsk, u64 cputime)
> {
> struct cpuacct *ca;
> int index = CPUACCT_STAT_SYSTEM;
> - struct pt_regs *regs = task_pt_regs(tsk);
> + struct pt_regs *regs = get_irq_regs() ? : task_pt_regs(tsk);
I've read the discussion in [1] but I don't think this approach is
correct either (and I don't know what is better :-/).
I only have a qualitative proof:
host:~ # uname -r
5.10.16-1-default
host:~ # systemd-run -p CPUAccounting=yes sh -c 'time sh -c "i=0 ; while [
\"\$i\" -lt 10000 ] ; do i=\$((\$i+1)) ; cat /proc/slabinfo >/dev/null ; done"
; sleep inf'
Running as unit: run-r101b9f53efcb4d2a9bfb65feb6f120ca.service
host:~ # cat
/sys/fs/cgroup/cpuacct/system.slice/run-r101b9f53efcb4d2a9bfb65feb6f120ca.service/cpuacct.usage{,_user,_sys}
16138535165
14332580468
1805954697
(See that sys/user ~ 0.1)
host:~ # journalctl -u run-r101b9f53efcb4d2a9bfb65feb6f120ca.service
-- Logs begin at Tue 2021-03-02 18:06:41 CET, end at Tue 2021-03-02 18:27:45
CET. --
Mar 02 18:27:29 host systemd[1]: Started /usr/bin/sh -c time sh -c "i=0 ; while
[ \"\$i\" -lt 10000 ] ; do i=\$((\$i+1)) ; cat /proc/slabinfo >/dev/null ;
done" ; sleep inf.
Mar 02 18:27:45 host sh[19117]: real 0m15.543s
Mar 02 18:27:45 host sh[19117]: user 0m10.752s
Mar 02 18:27:45 host sh[19117]: sys 0m5.379s
(See that sys/user ~ 0.5)
host:~ # cat
/sys/fs/cgroup/cpuacct/system.slice/run-r101b9f53efcb4d2a9bfb65feb6f120ca.service/cpuacct.stat
user 415
system 1209
(See that sys/user ~ 3.0 :-o)
The expectation is that significant amount of the loop is spent in
kernel (dumping slabinfo). I can't tell which of the ratios fits the
reality best but the cpuacct.usage_sys still seems too low.
Michal
[1]
https://lore.kernel.org/lkml/20200416141833.50663-1-songmuc...@bytedance.com/
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