linux-kernel - Re: [PATCH 1/4] softirq: implement IRQ flood detection mechanism

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Date:   Wed, 4 Sep 2019 10:38:59 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>,
        Ming Lei <ming.lei@...hat.com>
Cc:     Keith Busch <keith.busch@...el.com>,
        Hannes Reinecke <hare@...e.com>,
        Sagi Grimberg <sagi@...mberg.me>, linux-scsi@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Long Li <longli@...rosoft.com>,
        John Garry <john.garry@...wei.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-nvme@...ts.infradead.org, Jens Axboe <axboe@...com>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH 1/4] softirq: implement IRQ flood detection mechanism

On 9/4/19 10:31 AM, Daniel Lezcano wrote:
> On 04/09/2019 19:07, Bart Van Assche wrote:
>> Only if CONFIG_IRQ_TIME_ACCOUNTING has been enabled. However, I don't
>> know any Linux distro that enables that option. That's probably because
>> that option introduces two rdtsc() calls in each interrupt. Given the
>> overhead introduced by this option, I don't think this is the solution
>> Ming is looking for.
> 
> Was this overhead reported somewhere ?
  I think it is widely known that rdtsc is a relatively slow x86 
instruction. So I expect that using that instruction will cause a 
measurable overhead if it is called frequently enough. I'm not aware of 
any publicly available measurement data however.

Bart.