linux-kernel - Re: Proper kernel irq time accounting -v3

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Message-ID: <AANLkTimd0Acz3kcNswBoDS2XytfUgbE+ZyTxHUAcNspa@mail.gmail.com>
Date:	Thu, 30 Sep 2010 09:37:17 -0700
From:	Venkatesh Pallipadi <venki@...gle.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, Paul Turner <pjt@...gle.com>,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: Proper kernel irq time accounting -v3

On Thu, Sep 30, 2010 at 12:59 AM, Andi Kleen <andi@...stfloor.org> wrote:
> Venkatesh Pallipadi <venki@...gle.com> writes:
>>
>> Solution to (1) involves adding extra timing on irq entry/exit to
>> get the fine granularity info and then exporting it to user.
>
> This means RDTSC right?
>
> I am a bit concerned about overhead on systems with high TSC overhead.
> Is there a way to turn this off at runtime for those?
>

Yes. Overhead will be RDTSC.
notsc is a boot option that will disable this. I didn't want to have a
specific run time option to disable this as we would already have
other RDTSC users like native_sched_clock. Do you think we need a
specific option to disable this feature? I don't like adding a runtime
option because it complicates the code a bit (to handle things like
someone turning it off and turning it on later, etc).

Thanks,
Venki
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