Messages in this thread | | | Date | Fri, 27 Nov 2009 05:22:47 +0100 | From | Frederic Weisbecker <> | Subject | Re: PATCH: softlockup: Fix hung_task_check_count sysctl |
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On Fri, Nov 27, 2009 at 11:02:13AM +0800, Américo Wang wrote: > On Fri, Nov 27, 2009 at 10:55 AM, Frederic Weisbecker > <fweisbec@gmail.com> wrote: > > On Fri, Nov 27, 2009 at 10:46:53AM +0800, Américo Wang wrote: > >> On Fri, Nov 27, 2009 at 10:28 AM, Anton Blanchard <anton@samba.org> wrote: > >> > > >> > I'm seeing spikes of up to 0.5ms in khungtaskd on a large machine. To reduce > >> > this source of jitter I tried setting hung_task_check_count to 0: > >> > > >> > # echo 0 > /proc/sys/kernel/hung_task_check_count > >> > > >> > which didn't have the intended response. Change to a post increment of > >> > max_count, so a value of 0 means check 0 tasks. > >> > > >> > Signed-off-by: Anton Blanchard <anton@samba.org> > >> > >> > >> Ack. > >> > >> I would also suggest to make 'max_count' as unsigned long, > >> since sysctl_hung_task_check_count is. > >> > >> Thanks. > > > > > > Also, the batch_count thing should be dropped I think. > > This is a hardcoded, not overridable pause after 1024 > > threads checks to avoid latencies caused by rcu_read_lock. > > But now we have PREEMPT_RCU so people can enable it if > > they care about latency. We should remove it as it adds > > unnecessary complexity. > > This sounds OK for me. > > > > > I'm preparing a patch for that, on top of Anton patch. > > > > Great! > > Thanks.
Actually it looks like this check is not only there to take care of latency but also to avoid too much waiting before a grace period.
Hm, well, I'm not sure what to do.
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