Messages in this thread | | | Date | Wed, 10 Feb 2016 17:10:16 +0100 | From | Petr Mladek <> | Subject | Re: [PATCH] printk: avoid livelock if another CPU printks continuously |
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On Wed 2016-02-10 09:44:07, Steven Rostedt wrote: > On Wed, 10 Feb 2016 15:36:49 +0100 > Petr Mladek <pmladek@suse.com> wrote: > > > Bcc: > > Subject: Re: [PATCH] printk: avoid livelock if another CPU printks > > continuously > > Reply-To: > > In-Reply-To: <1454963703-20433-1-git-send-email-dvlasenk@redhat.com> > > > > Hmm, playing with mail headers?
Yeah. I am trying to do this reply back in the original thread.
> > > + /* Good, other CPU entered "for(;;)" loop */ > > > + goto out; > > > + } > > > + } > > > + /* No one seems to be willing to take it... */ > > > + if (console_trylock()) > > > + goto again; /* we took it */ > > > + /* Nope, someone else holds console_sem! Good */ > > > > The cycle gives a big chance other CPUs to enter console_unlock(). > > It means that more CPUs might end up in the above busy cycle. > > > > It gives a chance to move the printing to another CPU. It likely > > slows down the flood of messages because the producer end up > > here as well. > > > > So, it probably works but the performance is far from optimal. > > Many CPUs might end up doing nothing. I am afraid that this is > > not the right way to go. > > Note, it's not that performance critical, and the loop only happens if > someone else is adding to the console, which hopefully, should be rare.
I probably used too strong words. It is possible that the performance impact will not be critical. But the behavior is non-deterministic. I think that the approach taken by Jack is more promising. I mean the offloading of the console stuff to a workqueue.
Best Regards, Petr
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