lkml.org 
[lkml]   [2018]   [May]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [GIT PULL] isolation: 1Hz residual tick offloading v4
Date
Hi, Frederic!

>>>>> On Mon, 29 Jan 2018 02:10:26 +0100, Frederic Weisbecker wrote:
> On Wed, Jan 24, 2018 at 10:46:08AM -0500, Luiz Capitulino wrote:

[...]

>> Since the 1Hz tick offload worked for you, I must be missing
>> a way to disable this timer or the kernel is thinking my CPU
>> has unstable TSC (which it doesn't AFAIK).

> It's beyond the scope of this patchset but indeed that's
> right, I run my kernels with tsc=reliable because my CPUs
> don't have the TSC_RELIABLE flag. That's the only way I found
> to shutdown the tick completely on my test machine, otherwise
> I keep having that clocksource watchdog.

[...]

Thanks, it helps. But I have accounting problem:

if I run user busy loop on the nohz cpu, the task accounting works
correctly (top shows the task takes 100% cpu), but cpu accounting is
wrong (cpu is 100% idle, in the per-core view as well).

If I understand correctly, the stats are updated by account_user_time()
-> task_group_account_field() but there is no call for it in case of
offloading (it is called from irqtime_account_process_tick,
account_process_tick, vtime_user_exit).

Moreover, task_group_account_field() uses __this_cpu_add() which will be
wrong for offloading.

For testing I used kcpustat_cpu(task_cpu(p)) in
task_group_account_field() and added call account_user_time(curr, delta)
to the sched_tick_remote() what fixes it for me, but what would be the
proper fix?

--
WBR,
Yauheni Kaliuta

\
 
 \ /
  Last update: 2018-05-22 21:10    [W:0.102 / U:0.088 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site