From: Thomas Gleixner <tglx@linutronix.de>
To: Jeff Merkey <linux.mdb@gmail.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
John Stultz <john.stultz@linaro.org>
Subject: Re: [BUG REPORT] ktime_get_ts64 causes Hard Lockup
Date: Wed, 20 Jan 2016 10:21:53 +0100 (CET) [thread overview]
Message-ID: <alpine.DEB.2.11.1601201015000.3575@nanos> (raw)
In-Reply-To: <CAO6TR8V45TwC2YZF863o+Gaf5BboDaQg3+naV=qUNeXiRa4LPQ@mail.gmail.com>
On Tue, 19 Jan 2016, Jeff Merkey wrote:
> Nasty bug but trivial fix for this. What happens here is RAX (nsecs)
> gets set to a huge value (RAX = 0x17AE7F57C671EA7D) and passed through
And how exactly does that happen?
0x17AE7F57C671EA7D = 1.70644e+18 nsec
= 1.70644e+09 sec
= 2.84407e+07 min
= 474011 hrs
= 19750.5 days
= 54.1109 years
That's the real issue, not what you are trying to 'fix' in timespec_add_ns()
> Submitting a patch to fix this after I regress and test it. Since it
> makes no sense to loop on a simple calculation, fix should be:
>
> static __always_inline void timespec_add_ns(struct timespec *a, u64 ns)
> {
> a->tv_sec += div64_u64_rem(a->tv_nsec + ns, NSEC_PER_SEC, &ns);
> a->tv_nsec = ns;
> }
No. It's not that simple, because div64_u64_rem() is expensive on 32bit
architectures which have no hardware 64/32 division. And that's going to hurt
for the normal tick case where we have at max one iteration.
Thanks,
tglx
next prev parent reply other threads:[~2016-01-20 9:22 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-19 1:59 Jeff Merkey
2016-01-19 2:16 ` Jeff Merkey
2016-01-19 2:31 ` Jeff Merkey
2016-01-19 9:50 ` Thomas Gleixner
2016-01-19 15:37 ` Jeff Merkey
2016-01-19 22:00 ` Jeff Merkey
2016-01-20 0:59 ` Jeff Merkey
2016-01-20 9:21 ` Thomas Gleixner [this message]
2016-01-20 14:26 ` Thomas Gleixner
2016-01-20 16:40 ` Jeff Merkey
2016-01-20 16:53 ` Jeff Merkey
2016-01-20 17:16 ` Jeff Merkey
2016-01-20 17:32 ` John Stultz
2016-01-20 17:36 ` Jeff Merkey
2016-01-20 17:42 ` Thomas Gleixner
2016-01-20 17:59 ` John Stultz
2016-01-20 18:03 ` Jeff Merkey
2016-01-20 17:21 ` Thomas Gleixner
2016-01-20 17:33 ` Jeff Merkey
2016-01-20 19:34 ` Thomas Gleixner
2016-01-20 19:59 ` Jeff Merkey
2016-01-21 7:09 ` Jeff Merkey
2016-01-21 8:18 ` Jeff Merkey
2016-01-21 9:08 ` Jeff Merkey
2016-01-21 10:12 ` Thomas Gleixner
2016-01-21 15:46 ` Jeff Merkey
2016-01-21 16:57 ` Jeff Merkey
2016-01-21 17:00 ` Jeff Merkey
2016-01-21 17:07 ` Jeff Merkey
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=alpine.DEB.2.11.1601201015000.3575@nanos \
--to=tglx@linutronix.de \
--cc=john.stultz@linaro.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux.mdb@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox
all inboxes | Powered by JetHome®