From: Andrew Morton <akpm@linux-foundation.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
Waiman Long <longman@redhat.com>,
Matthew Wilcox <willy@infradead.org>,
Alexey Dobriyan <adobriyan@gmail.com>,
Kees Cook <keescook@chromium.org>,
linux-fsdevel@vger.kernel.org,
Davidlohr Bueso <dave@stgolabs.net>,
Miklos Szeredi <miklos@szeredi.hu>,
Daniel Colascione <dancol@google.com>,
Dave Chinner <david@fromorbit.com>,
Randy Dunlap <rdunlap@infradead.org>,
Marc Zyngier <marc.zyngier@arm.com>
Subject: Re: [patch V2 1/2] genriq: Avoid summation loops for /proc/stat
Date: Fri, 8 Feb 2019 14:32:55 -0800 [thread overview]
Message-ID: <20190208143255.9dec696b15f03bf00f4c60c2@linux-foundation.org> (raw)
In-Reply-To: <20190208135020.925487496@linutronix.de>
On Fri, 08 Feb 2019 14:48:03 +0100 Thomas Gleixner <tglx@linutronix.de> wrote:
> Waiman reported that on large systems with a large amount of interrupts the
> readout of /proc/stat takes a long time to sum up the interrupt
> statistics. In principle this is not a problem. but for unknown reasons
> some enterprise quality software reads /proc/stat with a high frequency.
>
> The reason for this is that interrupt statistics are accounted per cpu. So
> the /proc/stat logic has to sum up the interrupt stats for each interrupt.
>
> This can be largely avoided for interrupts which are not marked as
> 'PER_CPU' interrupts by simply adding a per interrupt summation counter
> which is incremented along with the per interrupt per cpu counter.
>
> The PER_CPU interrupts need to avoid that and use only per cpu accounting
> because they share the interrupt number and the interrupt descriptor and
> concurrent updates would conflict or require unwanted synchronization.
>
> ...
>
> --- a/include/linux/irqdesc.h
> +++ b/include/linux/irqdesc.h
> @@ -65,6 +65,7 @@ struct irq_desc {
> unsigned int core_internal_state__do_not_mess_with_it;
> unsigned int depth; /* nested irq disables */
> unsigned int wake_depth; /* nested wake enables */
> + unsigned int tot_count;
Confused. Isn't this going to quickly overflow?
next prev parent reply other threads:[~2019-02-08 22:33 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-08 13:48 [patch V2 0/2] genirq, proc: Speedup /proc/stat interrupt statistics Thomas Gleixner
2019-02-08 13:48 ` [patch V2 1/2] genriq: Avoid summation loops for /proc/stat Thomas Gleixner
2019-02-08 22:32 ` Andrew Morton [this message]
2019-02-08 22:46 ` Waiman Long
2019-02-08 23:21 ` Andrew Morton
2019-02-09 3:41 ` Matthew Wilcox
2019-02-13 15:55 ` David Laight
2019-02-08 13:48 ` [patch V2 2/2] proc/stat: Make the interrupt statistics more efficient Thomas Gleixner
2019-02-08 17:01 ` Alexey Dobriyan
2019-02-08 15:20 ` [patch V2 0/2] genirq, proc: Speedup /proc/stat interrupt statistics Waiman Long
2019-02-08 17:01 ` Davidlohr Bueso
2019-02-08 17:40 ` Marc Zyngier
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