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Re: [PATCH] [POWERPC] Improve (in|out)_beXX() asm code

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To: Benjamin Herrenschmidt <benh@...>
Cc: <linuxppc-dev@...>, <linux-kernel@...>, Scott Wood <scottwood@...>
Date: Tuesday, May 20, 2008 - 6:00 pm

On Tue, 20 May 2008, Benjamin Herrenschmidt wrote:

Depends on what you define as "necessary".  It's seem clear that I/O accessors
_no not_ need to be strictly ordered with respect to normal memory accesses,
by what's defined in memory-barriers.txt.  So if by "necessary" you mean what
the Linux standard for I/O accessors requires (and what other archs provide),
then yes, they have the necessary ordering guarantees.

But, if you want them to be strictly ordered w.r.t to normal memory, that's
not the case.

For example, in something like:

u32 *dmabuf = kmalloc(...);
...
dmabuf[0] = 1;
out_be32(&regs->dmactl, DMA_SEND_BUFFER);
dmabuf[0] = 2;
out_be32(&regs->dmactl, DMA_SEND_BUFFER);

gcc might decide to optimize this code to:

out_be32(&regs->dmactl, DMA_SEND_BUFFER);
out_be32(&regs->dmactl, DMA_SEND_BUFFER);
dmabuf[0] = 2;

gcc will often not do this optimization, because there might be aliasing
between "&regs->dmact" and "dmabuf", but it _can_ do it.  gcc can't optimize
the two identical out_be32's into one, or re-order them if they were to
different registers, but it can move the normal memory accesses around them.

Here's a quick hack I stuck in a driver to test.  compile with -save-temps and
check the resulting asm.  gcc will do the optimization I described above.

static void __iomem *baz = (void*)0x1234;
static struct bar {
     u32 bar[256];
} bar;

void foo(void) {
     bar.bar[0] = 44;
     out_be32(baz+100, 200);
     bar.bar[0] = 45;
     out_be32(baz+101, 201);
}
--
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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)
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