linux-kernel - Re: [RFC PATCH 2/3] softirq: implement interrupt flood detection

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Date:   Thu, 19 Dec 2019 11:43:47 +0100
From:   Daniel Wagner <dwagner@...e.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ming Lei <ming.lei@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
        linux-block@...r.kernel.org, Long Li <longli@...rosoft.com>,
        Ingo Molnar <mingo@...hat.com>, Christoph Hellwig <hch@....de>,
        Keith Busch <keith.busch@...el.com>,
        Sagi Grimberg <sagi@...mberg.me>,
        John Garry <john.garry@...wei.com>,
        Hannes Reinecke <hare@...e.com>
Subject: Re: [RFC PATCH 2/3] softirq: implement interrupt flood detection

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.