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Subject: Re: [PATCH 1/4] softirq: implement IRQ flood detection mechanism
To:     Daniel Lezcano <daniel.lezcano@linaro.org>,
        Ming Lei <ming.lei@redhat.com>
Cc:     Keith Busch <keith.busch@intel.com>,
        Hannes Reinecke <hare@suse.com>,
        Sagi Grimberg <sagi@grimberg.me>, linux-scsi@vger.kernel.org,
        Peter Zijlstra <peterz@infradead.org>,
        Long Li <longli@microsoft.com>,
        John Garry <john.garry@huawei.com>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-nvme@lists.infradead.org, Jens Axboe <axboe@fb.com>,
        Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Christoph Hellwig <hch@lst.de>
References: <20190827225827.GA5263@ming.t460p>
 <alpine.DEB.2.21.1908280104330.1939@nanos.tec.linutronix.de>
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 <alpine.DEB.2.21.1908281605190.23149@nanos.tec.linutronix.de>
 <20190903033001.GB23861@ming.t460p>
 <299fb6b5-d414-2e71-1dd2-9d6e34ee1c79@linaro.org>
 <20190903063125.GA21022@ming.t460p>
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 <dd96def4-1121-afbe-2431-9e516a06850c@linaro.org>
 <6f3b6557-1767-8c80-f786-1ea667179b39@acm.org>
 <2a8bd278-5384-d82f-c09b-4fce236d2d95@linaro.org>
From:   Bart Van Assche <bvanassche@acm.org>
Message-ID: <de16de12-fa1a-666c-ea19-fea5d096c1ca@acm.org>
Date:   Wed, 4 Sep 2019 10:38:59 -0700
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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.