linux-kernel - Re: [RFC] time: xtime

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Message-ID: <20110506171701.GJ11636@one.firstfloor.org>
Date:	Fri, 6 May 2011 19:17:01 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	john stultz <johnstul@...ibm.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Paul Mackerras <paulus@...ba.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Anton Blanchard <anton@...ba.org>, Ingo Molnar <mingo@...e.hu>
Subject: Re: [RFC] time: xtime_lock is held too long

> Unless I am very mistaken, it cannot explain my original report of up to
> 24.000 instructions waiting in ktime_get()

Yes it's a different problem. Sorry for hijacking your thread.

> 
> BTW, how many consecutive prefetch() a cpu can 'store/execute' before
> throwing away hints ?

It depends on the CPU. Older ones had a small number only. On the 
newer ones it tends to be limited by the various queues to memory,
which are a shared resource (so it also depends on what the other
threads/cores are doing)

I normally assume as a rule of thumb < 50

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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