From: Ming Lei <ming.lei@canonical.com>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Will Deacon <will.deacon@arm.com>,
"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: Fri, 17 Feb 2012 00:37:35 +0800 [thread overview]
Message-ID: <CACVXFVOygObWqPMLjg6uOB6inBkvvUjsQncNW0fbmpa4Xspw0Q@mail.gmail.com> (raw)
In-Reply-To: <1329409183.2293.245.camel@twins>
On Fri, Feb 17, 2012 at 12:19 AM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
> On Fri, 2012-02-17 at 00:12 +0800, Ming Lei wrote:
>> is triggered: u64 delta = 100 - 1000000 = 18446744073708551716.
>
> on x86 we do:
>
> int shift = 64 - x86_pmu.cntval_bits;
> s64 delta;
>
> delta = (new_raw_count << shift) - (prev_raw_count << shift);
> delta >>= shift;
>
> This deals with short overflows (on x86 the registers are typically 40
> or 48 bits wide). If the arm register is 32 you can of course also get
> there with some u32 casts.
Good idea, but it may not work if new_raw_count is bigger than prev_raw_count.
thanks
--
Ming Lei
next prev parent reply other threads:[~2012-02-16 16:37 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>
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[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 [this message]
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
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