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Date:   Thu, 19 Dec 2019 11:43:47 +0100
From:   Daniel Wagner <dwagner@suse.de>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Ming Lei <ming.lei@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Jens Axboe <axboe@kernel.dk>, linux-kernel@vger.kernel.org,
        linux-block@vger.kernel.org, Long Li <longli@microsoft.com>,
        Ingo Molnar <mingo@redhat.com>, Christoph Hellwig <hch@lst.de>,
        Keith Busch <keith.busch@intel.com>,
        Sagi Grimberg <sagi@grimberg.me>,
        John Garry <john.garry@huawei.com>,
        Hannes Reinecke <hare@suse.com>
Subject: Re: [RFC PATCH 2/3] softirq: implement interrupt flood detection
Message-ID: <20191219104347.ql6shgh2x7hk6iid@boron>
References: <20191218071942.22336-1-ming.lei@redhat.com>
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Hi,

On Thu, Dec 19, 2019 at 10:23:19AM +0100, Peter Zijlstra wrote:
> On Thu, Dec 19, 2019 at 09:59:48AM +0800, Ming Lei wrote:
> > > So pray tell, why did you not integrate this with IRQ_TIME_ACCOUNTING ?
> > > That already takes a timestamp and does most of what you need.
> > 
> > Yeah, that was the 1st approach I thought of, but IRQ_TIME_ACCOUNTING
> > may be disabled, and enabling it may cause observable effect on IO
> > performance.
> 
> Is that an actual concern, are people disabling it?

In SLE and openSUSE kernels it is disabled for x86_64 at this
point. And if I am not completely misstaken only x86_64 supports it at
this point. I was looking at enable_sched_clock_irqtime() which is
only called from x86_64.

Another thing I noticed get_util_irq() is defined in
kernel/sched/sched.h. I don't think the block/blq-mq.c driver should
include it direclty.

Thanks,
Daniel

ps: A customer observes the same problem as Ming is reporting.