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From: Will Deacon <will.deacon@arm.com>
To: Ming Lei <ming.lei@canonical.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>,
	"eranian@gmail.com" <eranian@gmail.com>,
	"Shilimkar, Santosh" <santosh.shilimkar@ti.com>,
	David Long <dave.long@linaro.org>,
	"b-cousson@ti.com" <b-cousson@ti.com>,
	"mans@mansr.com" <mans@mansr.com>,
	linux-arm <linux-arm-kernel@lists.infradead.org>,
	Ingo Molnar <mingo@elte.hu>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: oprofile and ARM A9 hardware counter
Date: Mon, 20 Feb 2012 09:44:14 +0000	[thread overview]
Message-ID: <20120220094414.GA13115@mudshark.cambridge.arm.com> (raw)
In-Reply-To: <CACVXFVOzoUYrn0SuqwBJ6rTmTNN1MxoR-45dv-owH2rcnQYLWg@mail.gmail.com>

On Mon, Feb 20, 2012 at 03:19:02AM +0000, Ming Lei wrote:
> On Fri, Feb 17, 2012 at 6:26 PM, Will Deacon <will.deacon@arm.com> wrote:
> > Not sure I follow. If the frequency is 10000, then we write 0xffffd8f0 to
> > the counter. That means we have a 0xffffd8f0 event window to read the
> 
> The frequency I described is the 'freq' from '-F freq'. On OMAP4, when
> the 'freq'
> is 10000 and the interval for one samle is 100us, the observed counter
> ('left' variable in armpmu_event_set_period) is about 90000, so the written
> value to the hw counter is 0xFFFEA06F, looks the window is wide enough,
> and we may not consider the issue in a737823d for sample-based profiling.

My mistake - I thought you were referring to a period of 10000, but similar
logic follows.

> > There's a trade off between allowing the counter to wrap back around past
> > its previous value or being able to handle overflow on a non-interrupt path.
> 
> I agree, it is not easy to read overflow flag and counter accurately
> from hardware
> directly on a non-interrupt path.
> 
> So do you need me to prepare a new patch, or you will do it by yourself?

If the last one I posted is alright to you (seems that it is), then I'll
update it with the removal of the overflow flag and post it to the list with
you on CC.

I also need to get to the bottom of those warnings.

Thanks,

Will

      reply	other threads:[~2012-02-20  9:44 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <1328578047.1724.17.camel@dave-Dell-System-XPS-L502X>
     [not found] ` <CAMQu2gwfo5JXAqQaLUNs7C7J3TUhEO2zOcyD0Rk-D_O61Yrfag@mail.gmail.com>
     [not found]   ` <CAMsRxfLNBbQO5XF+EHJqNsnW+s=ay3mjSV5dh=sxdwzktUu03g@mail.gmail.com>
     [not found]     ` <CAMQu2gzfNAwtf1c6jrTZpfGMSqBgBrQKmFTeCFzbvMh9ESBDUg@mail.gmail.com>
     [not found]       ` <CAMsRxfKR1ODH56BtcUT5Dv6qOVEYGVheEcW9ugXsZmLKok==bg@mail.gmail.com>
     [not found]         ` <CAMQu2gwWt6oQPjxc1YHgOoxVkHdck_q78Xf==7ncwRj0_uS-JQ@mail.gmail.com>
     [not found]           ` <CAMQu2gyCPtbNfBa5V8ve2JORN+sDeAY+hvR0g0_9U354JgcuiA@mail.gmail.com>
     [not found]             ` <CAMsRxfJVEgVJoHcaPQbMg5mwz=tZUce4oibDUxtnevSF8bGY9g@mail.gmail.com>
     [not found]               ` <CAMQu2gxVUqDF2HkPD=QeX0N_tUd=9FTd+T+1LHCR0tsCgQxC8Q@mail.gmail.com>
     [not found]                 ` <CAMsRxfJH+9MS=Svmh0BvDSb8xqsPe2HPobkeKcn8JO35npjhwQ@mail.gmail.com>
2012-02-08  2:24                   ` oprofile and ARM A9 hardware counter Ming Lei
2012-02-15 16:38                     ` Peter Zijlstra
2012-02-16 10:25                       ` Ming Lei
2012-02-16 15:00                         ` Will Deacon
2012-02-16 16:12                           ` Ming Lei
2012-02-16 16:19                             ` Peter Zijlstra
2012-02-16 16:37                               ` Ming Lei
2012-02-16 18:08                                 ` Will Deacon
2012-02-17  5:24                                   ` Ming Lei
2012-02-17 10:26                                     ` Will Deacon
2012-02-20  3:19                                       ` Ming Lei
2012-02-20  9:44                                         ` Will Deacon [this message]

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