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From: Peter Zijlstra <peterz@infradead.org>
To: Long Li <longli@microsoft.com>
Cc: "longli@linuxonhyperv.com" <longli@linuxonhyperv.com>,
	Ingo Molnar <mingo@redhat.com>,
	Keith Busch <keith.busch@intel.com>, Jens Axboe <axboe@fb.com>,
	Christoph Hellwig <hch@lst.de>, Sagi Grimberg <sagi@grimberg.me>,
	"linux-nvme@lists.infradead.org" <linux-nvme@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/3] sched: define a function to report the number of context switches on a CPU
Date: Wed, 21 Aug 2019 12:34:56 +0200	[thread overview]
Message-ID: <20190821103456.GY2349@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CY4PR21MB0741F33BBC800C0774CB8C15CEAA0@CY4PR21MB0741.namprd21.prod.outlook.com>

On Wed, Aug 21, 2019 at 08:20:48AM +0000, Long Li wrote:
> >>>Subject: Re: [PATCH 1/3] sched: define a function to report the number of
> >>>context switches on a CPU
> >>>
> >>>On Mon, Aug 19, 2019 at 11:14:27PM -0700, longli@linuxonhyperv.com
> >>>wrote:
> >>>> From: Long Li <longli@microsoft.com>
> >>>>
> >>>> The number of context switches on a CPU is useful to determine how
> >>>> busy this CPU is on processing IRQs. Export this information so it can
> >>>> be used by device drivers.
> >>>
> >>>Please do explain that; because I'm not seeing how number of switches
> >>>relates to processing IRQs _at_all_!
> 
> Some kernel components rely on context switch to progress, for example
> watchdog and RCU. On a CPU with reasonable interrupt load, it
> continues to make context switches, normally a number of switches per
> seconds. 

That isn't true; RCU is perfectly fine with a single task always running
and not making context switches, and so is the watchdog.

  reply	other threads:[~2019-08-21 10:35 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-20  6:14 [PATCH 0/3] fix interrupt swamp in NVMe longli
2019-08-20  6:14 ` [PATCH 1/3] sched: define a function to report the number of context switches on a CPU longli
2019-08-20  9:38   ` Peter Zijlstra
2019-08-21  8:20     ` Long Li
2019-08-21 10:34       ` Peter Zijlstra [this message]
2019-08-20  9:39   ` Peter Zijlstra
2019-08-20  6:14 ` [PATCH 2/3] sched: export idle_cpu() longli
2019-08-20  6:14 ` [PATCH 3/3] nvme: complete request in work queue on CPU with flooded interrupts longli
2019-08-20  9:52   ` Peter Zijlstra
2019-08-21  8:37     ` Long Li
2019-08-21 10:35       ` Peter Zijlstra
2019-08-20 17:33   ` Sagi Grimberg
2019-08-21  8:39     ` Long Li
2019-08-21 17:36       ` Long Li
2019-08-21 21:54         ` Sagi Grimberg
2019-08-24  0:13           ` Long Li
2019-08-23  3:21     ` Ming Lei
2019-08-24  0:27       ` Long Li
2019-08-24 12:55         ` Ming Lei
2019-08-20  8:25 ` [PATCH 0/3] fix interrupt swamp in NVMe Ming Lei
2019-08-20  8:59   ` John Garry
2019-08-20 15:05     ` Keith Busch
2019-08-21  7:47     ` Long Li
2019-08-21  9:44       ` Ming Lei
2019-08-21 10:03         ` John Garry
2019-08-21 16:27         ` Long Li
2019-08-22  1:33           ` Ming Lei
2019-08-22  2:00             ` Keith Busch
2019-08-22  2:23               ` Ming Lei
2019-08-22  9:48               ` Thomas Gleixner

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