linux-kernel - Re: [patch 0/2] genirq, proc: Speedup /proc/stat interrupt statistics

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Message-ID: <130dd9c2-38bd-b14b-fadc-09fadf2e8fc7@redhat.com>
Date:   Wed, 30 Jan 2019 22:46:21 -0500
From:   Waiman Long <longman@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Kees Cook <keescook@...omium.org>,
        linux-fsdevel@...r.kernel.org, Davidlohr Bueso <dave@...olabs.net>,
        Miklos Szeredi <miklos@...redi.hu>,
        Daniel Colascione <dancol@...gle.com>,
        Dave Chinner <david@...morbit.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Marc Zyngier <marc.zyngier@....com>
Subject: Re: [patch 0/2] genirq, proc: Speedup /proc/stat interrupt statistics

On 01/30/2019 05:00 PM, Thomas Gleixner wrote:
> On Wed, 30 Jan 2019, Andrew Morton wrote:
>> On Wed, 30 Jan 2019 13:31:30 +0100 Thomas Gleixner <tglx@...utronix.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.
>>>
>>> The following series addresses this by making the interrupt statitics code
>>> in the core generate the sum directly and by making the loop in the
>>> /proc/stat read function smarter.
>>>
>> Has the speedup been quantified?
> Waiman should be able to provide numbers
>
>
On a 4-socket IvyBridge-EX system (60-core 120-thread) and 3016 irqs, I
ran a test program that read /proc/stat 50,000 time. Before the patch,
the elapsed time was 18.436s (sys 18.380s). After the patch, it was
3.769s (sys 3.742s). It was an almost 80% reduction in execution time.
It was better than I expected. I like that.

Cheers,
Longman