[Top] [All Lists]

Re: Promblem with PREF (prefetching) in memcpy

To: Carsten Langgaard <>
Subject: Re: Promblem with PREF (prefetching) in memcpy
From: "Dr. David Alan Gilbert" <>
Date: Fri, 4 Oct 2002 13:35:54 +0100
Cc: Dominic Sweetman <>, Ralf Baechle <>,
In-reply-to: <>
Original-recipient: rfc822;
References: <> <> <>
User-agent: Mutt/1.4i
* Carsten Langgaard ( wrote:

> > For a Linux user program, at least, memory pages are "memory-like":
> > reads are guaranteed to be side-effect free, so any outlying
> > prefetches are harmless.  It's hard to see any circumstance where an
> > accessible cacheable location would lead to bad side-effects on read.
> What about an UART RX register, we might loose a character ?
> You can also configure you system, so you get a external interrupt from you
> system controller in case of a bus error, there is no way the CPU can
> relate this interrupt to the prefetching.

Well those woudn't be cacheable (hmm what happens to a prefetch on none
cached areas?) and also you could argue that you shouldn't be proding
UARTs from user space (although you could equally argue that it is
perfectly valid - but if you were doing it you probably wouldn't
be attacking them with a memcpy).

 ---------------- Have a happy GNU millennium! ----------------------   
/ Dr. David Alan Gilbert    | Running GNU/Linux on Alpha,68K| Happy  \ 
\ gro.gilbert @ | MIPS,x86,ARM, SPARC and HP-PA | In Hex /
 \ _________________________|_____   |_______/

<Prev in Thread] Current Thread [Next in Thread>