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([2a01:e34:ed2f:f020:ca2:9689:fa5d:1fea]) by smtp.googlemail.com with ESMTPSA id t13sm16071283wra.70.2019.09.03.00.50.06 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 03 Sep 2019 00:50:07 -0700 (PDT) Subject: Re: [PATCH 1/4] softirq: implement IRQ flood detection mechanism To: Ming Lei Cc: Thomas Gleixner , LKML , Long Li , Ingo Molnar , Peter Zijlstra , Keith Busch , Jens Axboe , Christoph Hellwig , Sagi Grimberg , John Garry , Hannes Reinecke , linux-nvme@lists.infradead.org, linux-scsi@vger.kernel.org References: <20190827225827.GA5263@ming.t460p> <20190828110633.GC15524@ming.t460p> <20190828135054.GA23861@ming.t460p> <20190903033001.GB23861@ming.t460p> <299fb6b5-d414-2e71-1dd2-9d6e34ee1c79@linaro.org> <20190903063125.GA21022@ming.t460p> <6b88719c-782a-4a63-db9f-bf62734a7874@linaro.org> <20190903072848.GA22170@ming.t460p> From: Daniel Lezcano Openpgp: preference=signencrypt Autocrypt: addr=daniel.lezcano@linaro.org; prefer-encrypt=mutual; keydata= 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a+0AjSGd886Bh0kT1Dznrite0dzYlTHlacbITZG84yRk/gS7DkYQdjL8zgFr/pxH5CbYJDk0 tYUhisTESeesbvWSPO5uNqqy1dAFw+dqRcF5gXIh3NKX0gqiAA87NM7nL5ym/CNpJ7z7nRC8 qePOXubgouxumi5RQs1+crBmCDa/AyJHKdG2mqCt9fx5EPbDpw6Zzx7hgURh4ikHoS7/tLjK iqWjuat8/HWc01yEd8rtkGuUcMqbCi1XhcAmkaOnX8FYscMRoyyMrWClRZEQRokqZIj79+PR adkDXtr4MeL8BaB7Ij2oyRVjXUwhFQNKi5Z5Rve0a3zvGkkqw8Mz20BOksjSWjAF6g9byukl CUVjC03PdMSufNLK06x5hPc/c4tFR4J9cLrV+XxdCX7r0zGos9SzTPGNuIk1LK++S3EJhLFj 4eoWtNhMWc1uiTf9ENza0ntqH9XBWEQ6IA1gubCniGG+Xg== Message-ID: Date: Tue, 3 Sep 2019 09:50:06 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190903072848.GA22170@ming.t460p> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-scsi-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org On 03/09/2019 09:28, Ming Lei wrote: > On Tue, Sep 03, 2019 at 08:40:35AM +0200, Daniel Lezcano wrote: >> On 03/09/2019 08:31, Ming Lei wrote: >>> Hi Daniel, >>> >>> On Tue, Sep 03, 2019 at 07:59:39AM +0200, Daniel Lezcano wrote: >>>> >>>> Hi Ming Lei, >>>> >>>> On 03/09/2019 05:30, Ming Lei wrote: >>>> >>>> [ ... ] >>>> >>>> >>>>>>> 2) irq/timing doesn't cover softirq >>>>>> >>>>>> That's solvable, right? >>>>> >>>>> Yeah, we can extend irq/timing, but ugly for irq/timing, since irq/timing >>>>> focuses on hardirq predication, and softirq isn't involved in that >>>>> purpose. >>>>> >>>>>> >>>>>>> Daniel, could you take a look and see if irq flood detection can be >>>>>>> implemented easily by irq/timing.c? >>>>>> >>>>>> I assume you can take a look as well, right? >>>>> >>>>> Yeah, I have looked at the code for a while, but I think that irq/timing >>>>> could become complicated unnecessarily for covering irq flood detection, >>>>> meantime it is much less efficient for detecting IRQ flood. >>>> >>>> In the series, there is nothing describing rigorously the problem (I can >>>> only guess) and why the proposed solution solves it. >>>> >>>> What is your definition of an 'irq flood'? A high irq load? An irq >>>> arriving while we are processing the previous one in the bottom halves? >>> >>> So far, it means that handling interrupt & softirq takes all utilization >>> of one CPU, then processes can't be run on this CPU basically, usually >>> sort of CPU lockup warning will be triggered. >> >> It is a scheduler problem then ? > > Scheduler can do nothing if the CPU is taken completely by handling > interrupt & softirq, so seems not a scheduler problem, IMO. Why? If there is a irq pressure on one CPU reducing its capacity, the scheduler will balance the tasks on another CPU, no? -- Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog