linux-kernel - Re: [PATCH] x86: Align jump targets to 1 byte boundaries

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Date:	Fri, 10 Apr 2015 11:32:18 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...nel.org>
CC:	Denys Vlasenko <dvlasenk@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jason Low <jason.low2@...com>,
	Peter Zijlstra <peterz@...radead.org>,
	Davidlohr Bueso <dave@...olabs.net>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Aswin Chandramouleeswaran <aswin@...com>,
	LKML <linux-kernel@...r.kernel.org>,
	Borislav Petkov <bp@...en8.de>,
	Andy Lutomirski <luto@...capital.net>,
	Brian Gerst <brgerst@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH] x86: Align jump targets to 1 byte boundaries

On 04/10/2015 10:54 AM, Ingo Molnar wrote:
> 
> Yeah, but the decoder stops if the prefetch crosses a cache line? So 
> it appears to be an interaction of the 16 byte prefetch window and 
> cache line boundaries?
> 

I don't think it has anything to do with cache lines.  Rather, you may
lose a cycle if the first instruction bundle crosses into a new 16-byte
chunk.

	-hpa

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