Re: MMIO and gcc re-ordering issue

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To: Trent Piepho <tpiepho@...>
Cc: Nick Piggin <nickpiggin@...>, Russell King <rmk+lkml@...>, Benjamin Herrenschmidt <benh@...>, David Miller <davem@...>, <linux-arch@...>, <scottwood@...>, <linuxppc-dev@...>, <alan@...>, <linux-kernel@...>
Date: Tuesday, June 3, 2008 - 3:07 pm

On Tue, 3 Jun 2008, Trent Piepho wrote:


With both registers in a WC+ area, yes. The write may be in the WC buffers 
until the WC buffers are flushed (short list: a fence, a serializing 
instruction, a read-write to uncached memory, or an interrupt. There are 
others, but those are the main ones).

But if the status register is in uncached memory (which is the only *sane* 
thing to do), then it doesn't matter if the control register is in WC 
memory. Because the status register read is itself serializing with the WC 
buffer, it's actually fine.

So this is used for putting things like ring queues in WC memory, and fill 
them up with writes, and get nice bursty write traffic with the CPU 
automatically buffering it up (think "stdio.h on a really low level"). And 
if you then have the command registers in UC memory or using IO port 
accesses, reading and writing to them will automatically serialize.


Not on x86.

And I don't care what anybody else says - x86 is *so* totally dominant, 
that other architectures have to live with the fact that 99.9% of all 
drivers are written for and tested on x86. As a result, anything else is 
"theory".

Are some drivers good and are careful? Yes. Are most? No, and even if they 
were, people making changes would mostly test them on x86. Architectures 
should strive to basically act as closely as possible to x86 semantics in 
order to not get nasty surprises.

And architectures that can't do that well enough *will* often find that 
they need to fix drivers, and only a small small subset of all kernel 
drivers will generally work out-of-the-box.

If you're ready to do that, your architecture can do anything it damn well 
pleases ;)

			Linus
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Messages in current thread:
[PATCH] [POWERPC] Improve (in|out)_beXX() asm code, Trent Piepho, (Tue May 20, 4:40 pm)
Re: [PATCH] [POWERPC] Improve (in|out)_beXX() asm code, Andreas Schwab, (Tue May 20, 6:00 pm)
Re: [PATCH] [POWERPC] Improve (in|out)_beXX() asm code, Trent Piepho, (Tue May 20, 6:11 pm)
Re: [PATCH] [POWERPC] Improve (in|out)_beXX() asm code, Andreas Schwab, (Tue May 20, 6:47 pm)
Re: [PATCH] [POWERPC] Improve (in|out)_beXX() asm code, Trent Piepho, (Tue May 20, 7:14 pm)
Re: [PATCH] [POWERPC] Improve (in|out)_beXX() asm code, Andreas Schwab, (Wed May 21, 4:03 am)
Re: [PATCH] [POWERPC] Improve (in|out)_beXX() asm code, Trent Piepho, (Wed May 21, 4:25 pm)
Re: [PATCH] [POWERPC] Improve (in|out)_beXX() asm code, Benjamin Herrenschmidt, (Tue May 20, 5:16 pm)
Re: [PATCH] [POWERPC] Improve (in|out)_beXX() asm code, Trent Piepho, (Tue May 20, 6:00 pm)
Re: [PATCH] [POWERPC] Improve (in|out)_beXX() asm code, Benjamin Herrenschmidt, (Wed May 21, 10:00 am)
Re: [PATCH] [POWERPC] Improve (in|out)_beXX() asm code, Trent Piepho, (Wed May 21, 3:44 pm)
Re: [PATCH] [POWERPC] Improve (in|out)_beXX() asm code, Benjamin Herrenschmidt, (Wed May 21, 4:41 pm)
Re: [PATCH] [POWERPC] Improve (in|out)_beXX() asm code, Trent Piepho, (Tue May 20, 6:55 pm)
Re: [PATCH] [POWERPC] Improve (in|out)_beXX() asm code, Benjamin Herrenschmidt, (Wed May 21, 10:01 am)
Re: [PATCH] [POWERPC] Improve (in|out)_beXX() asm code, David Miller, (Tue May 20, 6:39 pm)
Re: [PATCH] [POWERPC] Improve (in|out)_beXX() asm code, David Miller, (Tue May 20, 6:53 pm)
Re: [PATCH] [POWERPC] Improve (in|out)_beXX() asm code, Benjamin Herrenschmidt, (Fri May 23, 12:24 am)
Re: [PATCH] [POWERPC] Improve (in|out)_beXX() asm code, Trent Piepho, (Thu May 22, 6:56 pm)
MMIO and gcc re-ordering issue, Benjamin Herrenschmidt, (Mon May 26, 9:33 pm)
Re: MMIO and gcc re-ordering issue, Jonathan Corbet, (Tue May 27, 11:28 am)
Re: MMIO and gcc re-ordering issue, David Miller, (Mon May 26, 9:40 pm)
Re: MMIO and gcc re-ordering issue, Benjamin Herrenschmidt, (Mon May 26, 10:15 pm)
Re: MMIO and gcc re-ordering issue, David Miller, (Mon May 26, 10:28 pm)
Re: MMIO and gcc re-ordering issue, Alan Cox, (Tue May 27, 4:24 am)
Re: MMIO and gcc re-ordering issue, Arjan van de Ven, (Mon May 26, 11:42 pm)
Re: MMIO and gcc re-ordering issue, Benjamin Herrenschmidt, (Tue May 27, 3:08 am)
Re: MMIO and gcc re-ordering issue, Roland Dreier, (Tue May 27, 11:50 am)
Re: MMIO and gcc re-ordering issue, Pavel Machek, (Sat May 31, 4:04 am)
Re: MMIO and gcc re-ordering issue, Benjamin Herrenschmidt, (Tue May 27, 5:11 pm)
Re: MMIO and gcc re-ordering issue, Roland Dreier, (Tue May 27, 5:33 pm)
Re: MMIO and gcc re-ordering issue, Jes Sorensen, (Thu May 29, 10:47 am)
Re: MMIO and gcc re-ordering issue, Jeremy Higdon, (Sat May 31, 3:52 am)
Re: MMIO and gcc re-ordering issue, Jes Sorensen, (Mon Jun 2, 5:56 am)
Re: MMIO and gcc re-ordering issue, Nick Piggin, (Tue Jun 3, 12:33 am)
Re: MMIO and gcc re-ordering issue, Jesse Barnes, (Tue Jun 3, 12:52 pm)
Re: MMIO and gcc re-ordering issue, Jes Sorensen, (Thu Jun 5, 4:40 am)
Re: MMIO and gcc re-ordering issue, Benjamin Herrenschmidt, (Thu Jun 5, 4:43 am)
Re: MMIO and gcc re-ordering issue, Matthew Wilcox, (Thu Jun 12, 11:07 am)
Re: MMIO and gcc re-ordering issue, Benjamin Herrenschmidt, (Thu Jun 12, 8:07 pm)
Re: MMIO and gcc re-ordering issue, Jeremy Higdon, (Tue Jun 3, 4:15 am)
Re: MMIO and gcc re-ordering issue, Nick Piggin, (Tue Jun 3, 4:19 am)
Re: MMIO and gcc re-ordering issue, Jeremy Higdon, (Tue Jun 3, 4:45 am)
Re: MMIO and gcc re-ordering issue, Jeremy Higdon, (Mon Jun 2, 5:02 pm)
Re: MMIO and gcc re-ordering issue, Roland Dreier, (Thu May 29, 6:06 pm)
Re: MMIO and gcc re-ordering issue, Trent Piepho, (Thu May 29, 6:25 pm)
Re: MMIO and gcc re-ordering issue, Paul Mackerras, (Thu May 29, 11:56 pm)
Re: MMIO and gcc re-ordering issue, Benjamin Herrenschmidt, (Thu May 29, 5:40 pm)
Re: MMIO and gcc re-ordering issue, Jes Sorensen, (Fri May 30, 5:48 am)
Re: MMIO and gcc re-ordering issue, Pavel Machek, (Sat May 31, 4:14 am)
Re: MMIO and gcc re-ordering issue, Jes Sorensen, (Mon Jun 2, 5:48 am)
Re: MMIO and gcc re-ordering issue, Jesse Barnes, (Thu May 29, 5:53 pm)
Re: MMIO and gcc re-ordering issue, Jes Sorensen, (Fri May 30, 5:39 am)
Re: MMIO and gcc re-ordering issue, Trent Piepho, (Thu May 29, 5:48 pm)
Re: MMIO and gcc re-ordering issue, Benjamin Herrenschmidt, (Thu May 29, 6:05 pm)
Re: MMIO and gcc re-ordering issue, Trent Piepho, (Thu May 29, 9:53 pm)
Re: MMIO and gcc re-ordering issue, James Bottomley, (Thu May 29, 11:01 am)
Re: MMIO and gcc re-ordering issue, Jes Sorensen, (Fri May 30, 5:36 am)
Re: MMIO and gcc re-ordering issue, Jesse Barnes, (Fri May 30, 1:21 pm)
Re: MMIO and gcc re-ordering issue, Jeremy Higdon, (Sat May 31, 3:57 am)
Re: MMIO and gcc re-ordering issue, Benjamin Herrenschmidt, (Tue May 27, 6:13 pm)
Re: MMIO and gcc re-ordering issue, Roland Dreier, (Tue May 27, 6:39 pm)
Re: MMIO and gcc re-ordering issue, James Bottomley, (Tue May 27, 12:37 pm)
Re: MMIO and gcc re-ordering issue, Roland Dreier, (Tue May 27, 1:38 pm)
Re: MMIO and gcc re-ordering issue, James Bottomley, (Tue May 27, 1:53 pm)
Re: MMIO and gcc re-ordering issue, Roland Dreier, (Tue May 27, 2:07 pm)
Re: MMIO and gcc re-ordering issue, Chris Friesen, (Tue May 27, 5:23 pm)
Re: MMIO and gcc re-ordering issue, Paul Mackerras, (Tue May 27, 7:04 pm)
Re: MMIO and gcc re-ordering issue, Roland Dreier, (Tue May 27, 5:29 pm)
Re: MMIO and gcc re-ordering issue, Roland Dreier, (Tue May 27, 2:17 pm)
Re: MMIO and gcc re-ordering issue, Roland Dreier, (Tue May 27, 12:08 am)
Re: MMIO and gcc re-ordering issue, Arjan van de Ven, (Tue May 27, 12:20 am)
Re: MMIO and gcc re-ordering issue, Benjamin Herrenschmidt, (Mon May 26, 11:39 pm)
Re: MMIO and gcc re-ordering issue, Linus Torvalds, (Tue May 27, 11:35 am)
Re: MMIO and gcc re-ordering issue, Benjamin Herrenschmidt, (Tue May 27, 5:10 pm)
Re: MMIO and gcc re-ordering issue, Linus Torvalds, (Tue May 27, 5:30 pm)
Re: MMIO and gcc re-ordering issue, Alan Cox, (Tue May 27, 5:38 pm)
Re: MMIO and gcc re-ordering issue, Linus Torvalds, (Tue May 27, 5:59 pm)
Re: MMIO and gcc re-ordering issue, Matthew Wilcox, (Tue May 27, 5:53 pm)
Re: MMIO and gcc re-ordering issue, Linus Torvalds, (Tue May 27, 6:02 pm)
Re: MMIO and gcc re-ordering issue, Alan Cox, (Tue May 27, 5:46 pm)
Re: MMIO and gcc re-ordering issue, Benjamin Herrenschmidt, (Tue May 27, 5:38 pm)
Re: MMIO and gcc re-ordering issue, Linus Torvalds, (Tue May 27, 5:55 pm)
Re: MMIO and gcc re-ordering issue, Russell King, (Mon Jun 2, 3:24 am)
Re: MMIO and gcc re-ordering issue, Nick Piggin, (Tue Jun 3, 12:16 am)
Re: MMIO and gcc re-ordering issue, Trent Piepho, (Tue Jun 3, 3:43 pm)
Re: MMIO and gcc re-ordering issue, Benjamin Herrenschmidt, (Tue Jun 3, 6:26 pm)
Re: MMIO and gcc re-ordering issue, Matthew Wilcox, (Tue Jun 3, 5:33 pm)
Re: MMIO and gcc re-ordering issue, Trent Piepho, (Tue Jun 3, 5:44 pm)
Re: MMIO and gcc re-ordering issue, Nick Piggin, (Tue Jun 3, 10:25 pm)
Re: MMIO and gcc re-ordering issue, Trent Piepho, (Wed Jun 4, 2:39 am)
Re: MMIO and gcc re-ordering issue, Linus Torvalds, (Tue Jun 3, 10:47 am)
Re: MMIO and gcc re-ordering issue, Nick Piggin, (Tue Jun 3, 10:19 pm)
Re: MMIO and gcc re-ordering issue, Trent Piepho, (Tue Jun 3, 2:47 pm)
Re: MMIO and gcc re-ordering issue, Linus Torvalds, (Tue Jun 3, 3:07 pm)
Re: MMIO and gcc re-ordering issue, Nick Piggin, (Tue Jun 10, 2:56 am)
Re: MMIO and gcc re-ordering issue, Paul Mackerras, (Wed Jun 11, 1:20 am)
Re: MMIO and gcc re-ordering issue, Paul Mackerras, (Wed Jun 11, 12:18 am)
Re: MMIO and gcc re-ordering issue, Nick Piggin, (Wed Jun 11, 1:00 am)
Re: MMIO and gcc re-ordering issue, Linus Torvalds, (Wed Jun 11, 10:46 am)
Re: MMIO and gcc re-ordering issue, Paul Mackerras, (Wed Jun 11, 1:13 am)
Re: MMIO and gcc re-ordering issue, Nick Piggin, (Wed Jun 11, 1:35 am)
Re: MMIO and gcc re-ordering issue, Paul Mackerras, (Thu Jun 12, 8:14 am)
Re: MMIO and gcc re-ordering issue, Nick Piggin, (Thu Jun 12, 9:08 am)
Re: MMIO and gcc re-ordering issue, Nick Piggin, (Wed Jun 11, 2:02 am)
Re: MMIO and gcc re-ordering issue, Jesse Barnes, (Tue Jun 10, 1:41 pm)
Re: MMIO and gcc re-ordering issue, James Bottomley, (Tue Jun 10, 2:10 pm)
Re: MMIO and gcc re-ordering issue, Roland Dreier, (Tue Jun 10, 3:05 pm)
Re: MMIO and gcc re-ordering issue, Jesse Barnes, (Tue Jun 10, 3:19 pm)
Re: MMIO and gcc re-ordering issue, Nick Piggin, (Tue Jun 10, 11:29 pm)
Re: MMIO and gcc re-ordering issue, Jesse Barnes, (Wed Jun 11, 12:07 pm)
Re: MMIO and gcc re-ordering issue, Nick Piggin, (Thu Jun 12, 7:27 am)
Re: MMIO and gcc re-ordering issue, Benjamin Herrenschmidt, (Tue Jun 10, 11:40 pm)
Re: MMIO and gcc re-ordering issue, Nick Piggin, (Wed Jun 11, 12:06 am)
Re: MMIO and gcc re-ordering issue, Nick Piggin, (Tue Jun 3, 10:05 pm)
Re: MMIO and gcc re-ordering issue, Linus Torvalds, (Tue Jun 3, 10:46 pm)
Re: MMIO and gcc re-ordering issue, Alan Cox, (Wed Jun 4, 7:47 am)
Re: MMIO and gcc re-ordering issue, Matthew Wilcox, (Tue Jun 3, 2:55 pm)
Re: MMIO and gcc re-ordering issue, Trent Piepho, (Tue Jun 3, 3:57 pm)
Re: MMIO and gcc re-ordering issue, Matthew Wilcox, (Tue Jun 3, 5:35 pm)
Re: MMIO and gcc re-ordering issue, Trent Piepho, (Tue Jun 3, 5:58 pm)
Re: MMIO and gcc re-ordering issue, Nick Piggin, (Tue Jun 3, 10:00 pm)
Re: MMIO and gcc re-ordering issue, Benjamin Herrenschmidt, (Tue Jun 3, 12:32 am)
Re: MMIO and gcc re-ordering issue, Nick Piggin, (Tue Jun 3, 2:11 am)
Re: MMIO and gcc re-ordering issue, Paul Mackerras, (Tue Jun 3, 2:53 am)
Re: MMIO and gcc re-ordering issue, Nick Piggin, (Tue Jun 3, 3:18 am)
Re: MMIO and gcc re-ordering issue, Benjamin Herrenschmidt, (Tue Jun 3, 2:48 am)
Re: MMIO and gcc re-ordering issue, Benjamin Herrenschmidt, (Tue May 27, 6:19 pm)
Re: MMIO and gcc re-ordering issue, Arnd Bergmann, (Thu May 29, 3:10 am)
Re: MMIO and gcc re-ordering issue, Alan Cox, (Thu May 29, 6:46 am)
Re: MMIO and gcc re-ordering issue, Matthew Wilcox, (Tue May 27, 5:42 pm)
Re: MMIO and gcc re-ordering issue, Benjamin Herrenschmidt, (Tue May 27, 6:17 pm)
Re: MMIO and gcc re-ordering issue, Haavard Skinnemoen, (Wed May 28, 4:36 am)
Re: MMIO and gcc re-ordering issue, Benjamin Herrenschmidt, (Thu May 29, 9:13 pm)
Re: MMIO and gcc re-ordering issue, Haavard Skinnemoen, (Fri May 30, 2:07 am)
Re: MMIO and gcc re-ordering issue, Benjamin Herrenschmidt, (Fri May 30, 3:24 am)
Re: MMIO and gcc re-ordering issue, Haavard Skinnemoen, (Fri May 30, 4:27 am)
Re: MMIO and gcc re-ordering issue, Geert Uytterhoeven, (Fri May 30, 5:22 am)
Re: MMIO and gcc re-ordering issue, Haavard Skinnemoen, (Mon Jun 2, 4:11 am)
Re: MMIO and gcc re-ordering issue, Linus Torvalds, (Wed Jun 4, 11:31 am)
Re: MMIO and gcc re-ordering issue, Scott Wood, (Mon Jun 2, 11:48 am)
Re: MMIO and gcc re-ordering issue, Haavard Skinnemoen, (Tue Jun 3, 3:46 am)
Re: MMIO and gcc re-ordering issue, Pantelis Antoniou, (Thu May 29, 7:05 am)
Re: MMIO and gcc re-ordering issue, Trent Piepho, (Tue May 27, 2:23 pm)
Re: MMIO and gcc re-ordering issue, Scott Wood, (Tue May 27, 2:33 pm)
Re: MMIO and gcc re-ordering issue, Linus Torvalds, (Tue May 27, 12:47 pm)
Re: MMIO and gcc re-ordering issue, Benjamin Herrenschmidt, (Tue May 27, 5:12 pm)
Re: MMIO and gcc re-ordering issue, Linus Torvalds, (Tue May 27, 1:31 pm)
Re: MMIO and gcc re-ordering issue, Ingo Molnar, (Mon Jun 2, 6:36 am)
Re: MMIO and gcc re-ordering issue, Benjamin Herrenschmidt, (Mon Jun 2, 5:53 pm)
MMIO and gcc re-ordering (Was: [PATCH] [POWERPC] Improve (in..., Benjamin Herrenschmidt, (Fri May 23, 8:36 am)
Re: MMIO and gcc re-ordering (Was: [PATCH] [POWERPC] Improve..., Benjamin Herrenschmidt, (Fri May 23, 8:50 am)
Re: MMIO and gcc re-ordering (Was: [PATCH] [POWERPC] Improve..., Benjamin Herrenschmidt, (Fri May 23, 6:47 pm)
Re: [PATCH] [POWERPC] Improve (in|out)_beXX() asm code, Benjamin Herrenschmidt, (Tue May 20, 6:02 pm)
Re: [PATCH] [POWERPC] Improve (in|out)_beXX() asm code, Trent Piepho, (Tue May 20, 6:21 pm)