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Date: Fri, 10 Apr 2015 11:32:18 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Ingo Molnar <mingo@kernel.org>
CC: Denys Vlasenko <dvlasenk@redhat.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Jason Low <jason.low2@hp.com>, Peter Zijlstra <peterz@infradead.org>,
        Davidlohr Bueso <dave@stgolabs.net>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Aswin Chandramouleeswaran <aswin@hp.com>,
        LKML <linux-kernel@vger.kernel.org>, Borislav Petkov <bp@alien8.de>,
        Andy Lutomirski <luto@amacapital.net>, Brian Gerst <brgerst@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [PATCH] x86: Align jump targets to 1 byte boundaries
References: <CA+55aFwZWi6ecDmVsMBQJTrgrW3GD2DaRtpiOspe=5amR1=dNg@mail.gmail.com> <20150409183926.GM6464@linux.vnet.ibm.com> <20150410090051.GA28549@gmail.com> <20150410091252.GA27630@gmail.com> <20150410092152.GA21332@gmail.com> <20150410111427.GA30477@gmail.com> <20150410112748.GB30477@gmail.com> <20150410120846.GA17101@gmail.com> <5527C700.3030405@redhat.com> <5527CD92.1080901@zytor.com> <20150410175407.GB6563@gmail.com>
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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