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From: David Woodhouse <dwmw2@infradead.org>
To: Linus Torvalds <torvalds@transmeta.com>
Cc: Peter Rival <frival@zk3.dec.com>,
	paulus@samba.org, "Martin J. Bligh" <Martin.Bligh@us.ibm.com>,
	Alan Cox <alan@lxorguk.ukuu.org.uk>,
	linux-kernel@vger.kernel.org, jay.estabrook@compaq.com,
	rth@twiddle.net
Subject: Re: [PATCH] change name of rep_nop
Date: Tue, 09 Oct 2001 01:03:22 +0100	[thread overview]
Message-ID: <15753.1002585802@redhat.com> (raw)
In-Reply-To: <Pine.LNX.4.33.0110081643230.1064-100000@penguin.transmeta.com>
In-Reply-To: <Pine.LNX.4.33.0110081643230.1064-100000@penguin.transmeta.com>


torvalds@transmeta.com said:
> There's no way we should implement "simon_says".
> There's a difference between stupiud hardware changing memory from
> under us through mapping tricks, and cache coherency in general.

True. Although for simplicity's sake I wasn't talking about the mapping 
tricks, this was just for writing/erasing flash chips without doing any 
paging - it you're mapping different chips into the same hole you need the 
same cache-flush tricks even for read-only chips.

> What you want is the "memory_went_away_from_us()" kind of cache flush,
> which has nothing at all to do with cache coherency. And it should be
> explicitly and clearly named THAT

As you wish. How about:

void memory_went_away_from_us(void);
 and
void memory_range_went_away_from_us(unsigned long start, unsigned long len);

Where 'start' is an ioremap cookie.

> and you should not blame the fact that x86 is always 100% cache coherent
> and that the normal cache coherency routines should _never_ be anything
> but a nop.

Indeed. That's eminently sane - it was just the nomenclature and the 
documentation which was less so.

> Also note that wbinvd is known to corrupted the caches and lead to
> lockups on certain x86 cores. You need to be a _lot_ more careful than
> just doing it indiscriminately from a driver.

Yeah - but x86 isn't a particularly interesting architecture in this
context. If you can't selectively flush a range, you'll probably find that
you haven't gained enough from being able to do burst reads to offset the
cost of the complete cache flushes.

--
dwmw2



  reply	other threads:[~2001-10-09  0:03 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2001-10-05 10:46 Paul Mackerras
2001-10-05 14:37 ` Alan Cox
2001-10-05 18:06   ` Peter Rival
2001-10-05 23:28   ` Paul Mackerras
2001-10-05 23:54     ` Martin J. Bligh
2001-10-06  1:40     ` Paul Mackerras
2001-10-08 19:27       ` Peter Rival
2001-10-08 22:36       ` David Woodhouse
2001-10-08 22:49         ` Alan Cox
2001-10-08 23:06         ` David Woodhouse
2001-10-08 23:42           ` David Woodhouse
2001-10-08 23:46           ` David S. Miller
2001-10-08 23:08         ` David S. Miller
2001-10-08 23:46         ` Linus Torvalds
2001-10-09  0:03           ` David Woodhouse [this message]
2001-10-08 22:46       ` David S. Miller
2001-10-08 23:16         ` Alan Cox
2001-10-08 23:24           ` Dave Jones
2001-10-08 23:33             ` Alan Cox
2001-10-09  5:01             ` George Greer
2001-10-08 23:30           ` David S. Miller
2001-10-09 10:33           ` Benjamin Herrenschmidt
2001-10-09 11:30             ` Keith Owens
2001-10-09 12:13               ` Benjamin Herrenschmidt
2001-10-09 12:15               ` Alan Cox
2001-10-09  8:51 Etienne Lorrain
2001-10-09 11:30 ` Alan Cox

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