linux-kernel - Re: [PATCH RFC] pvclock: Make pv_clock more robust and fixup it if overflow happens

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Date:	Mon, 13 Feb 2012 19:15:07 +0100
From:	Igor Mammedov <imammedo@...hat.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
CC:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	x86@...nel.org, jacob.jun.pan@...ux.intel.com,
	alan@...ux.intel.com, feng.tang@...el.com, konrad.wilk@...cle.com,
	avi@...hat.com, glommer@...hat.com, johnstul@...ibm.com,
	riel@...hat.com, tj@...nel.org, kosaki.motohiro@...fujitsu.com,
	akpm@...ux-foundation.org, amit.shah@...hat.com
Subject: Re: [PATCH RFC] pvclock: Make pv_clock more robust and fixup it if
 overflow happens

On 02/13/2012 06:48 PM, Marcelo Tosatti wrote:
> On Mon, Feb 13, 2012 at 04:45:59PM +0100, Igor Mammedov wrote:
>> Instead of hunting misterious stalls/hungs all over the kernel when
>> overflow occurs at pvclock.c:pvclock_get_nsec_offset
>>
>>      u64 delta = native_read_tsc() - shadow->tsc_timestamp;
>>
>> and introducing hooks when places of unexpected access found, pv_clock
>> should be initialized for the calling cpu if overflow condition is detected.
>>
>> Signed-off-by: Igor Mammedov<imammedo@...hat.com>
>
> Igor,
>
> I disagree. This is fixing the symptom not the root cause. Additionally,
> Xen also uses pvclock_clocksource_read.
>
> How about adding a BUG_ON to detect the overflow, this way hunting for
> the problem is not necessary.
>
Ok, I'll repost bug_on version.
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