linux-kernel - Re: [Query] Ticks happen in pair for NO_HZ

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 18 Dec 2013 10:08:19 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Kevin Hilman <khilman@...aro.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>,
	Linaro Networking <linaro-networking@...aro.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Tejun Heo <tj@...nel.org>
Subject: Re: [Query] Ticks happen in pair for NO_HZ_FULL cores ?

On 17 December 2013 22:05, Kevin Hilman <khilman@...aro.org> wrote:
> For future reference, for generating email friendly trace output for
> discussion like this, you can use something like:
>
>    trace-cmd report --cpu=1 trace.dat

Okay..

>> And after that the next event comes after 5 Seconds.
>>
>> And so I was talking for the Event 41.
>
> That first event (Event 41) is an interrupt, and comes from the
> scheduler tick.  The tick is happening because the writeback workqueue
> just ran and we're not in NO_HZ mode.

This is what I was trying to ask. Why can't we enter in NO_HZ_FULL mode
as soon as writeback workqueue just ran? That way we can go into NOHZ
mode earlier..

> However, as soon as that IRQ (and resulting softirqs) are finished, we
> enter NO_HZ mode again.  But as you mention, it only lasts for ~5 sec
> when the timer fires again.  Once again, it fires because of the
> writeback workqueue, and soon therafter it switches back to NO_HZ mode
> again.

That's fine.. It wasn't part of my query :) .. But yes your trick
would be useful
for my usecase :)
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/