From: Peter Zijlstra <peterz@infradead.org>
To: Dave Hansen <dave.hansen@linux.intel.com>
Cc: mingo@kernel.org, hpa@zytor.com, linux-kernel@vger.kernel.org,
tglx@linutronix.de, dzickus@redhat.com,
linux-tip-commits@vger.kernel.org
Subject: Re: [tip:perf/core] x86/nmi: Push duration printk() to irq context
Date: Mon, 10 Feb 2014 18:05:26 +0100 [thread overview]
Message-ID: <20140210170526.GP9987@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <52F9021C.1030801@linux.intel.com>
On Mon, Feb 10, 2014 at 08:45:16AM -0800, Dave Hansen wrote:
> On 02/10/2014 05:29 AM, tip-bot for Peter Zijlstra wrote:
> > x86/nmi: Push duration printk() to irq context
> >
> > Calling printk() from NMI context is bad (TM), so move it to IRQ
> > context.
>
> Bad since the I/O device that we're doing it to may be slow and make the
> NMI painfully long?
>
> I can see why it might be a bad idea, but I'm unsold that it is
> *universally* a bad idea.
printk() takes locks, NMI interrupts printk lock and tries to printk.
you get to keep pieces.
> > In doing so we slightly change (probably wreck) the debugfs
> > nmi_longest_ns thingy, in that it doesn't update to reflect the
> > longest, nor does writing to it reset the count.
>
> The reason I coded this up was that NMIs were firing off so fast that
> nothing else was getting a chance to run. With this patch, at least the
> printk() would come out and I'd have some idea what was going on.
Ah indeed, in which case you don't get to run the irq_work. But you
really shouldn't do printk() from NMI and esp. not in a case that
regularly and reliably triggers for everyone and is not a hardware
error.
next prev parent reply other threads:[~2014-02-10 17:05 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-02-10 13:29 [tip:perf/core] x86/nmi: Push duration printk() to irq context tip-bot for Peter Zijlstra
2014-02-10 16:45 ` Dave Hansen
2014-02-10 17:05 ` Peter Zijlstra [this message]
2014-02-11 15:01 ` Peter Zijlstra
2014-02-11 16:44 ` Dave Hansen
2014-02-21 21:12 ` [tip:perf/core] perf/x86: Warn to early_printk() in case irq_work is too slow tip-bot for Peter Zijlstra
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=20140210170526.GP9987@twins.programming.kicks-ass.net \
--to=peterz@infradead.org \
--cc=dave.hansen@linux.intel.com \
--cc=dzickus@redhat.com \
--cc=hpa@zytor.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-tip-commits@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=tglx@linutronix.de \
/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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.