linux-kernel - Re: [SUGGESTION]: drop virtual merge accounting in I/O requests

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Message-ID: <Pine.LNX.4.64.0807151830290.22181@devserv.devel.redhat.com>
Date:	Tue, 15 Jul 2008 18:32:37 -0400 (EDT)
From:	Mikulas Patocka <mpatocka@...hat.com>
To:	David Miller <davem@...emloft.net>
cc:	andi@...stfloor.org, sparclinux@...r.kernel.org,
	linux-kernel@...r.kernel.org, jens.axboe@...cle.com
Subject: Re: [SUGGESTION]: drop virtual merge accounting in I/O requests

On Mon, 14 Jul 2008, David Miller wrote:

> From: Mikulas Patocka <mpatocka@...hat.com>
> Date: Mon, 14 Jul 2008 19:16:17 -0400 (EDT)
> 
> > So the question is: to reduce number of requests by 12% on an outdated 
> > SCSI card, it is sensible to maintain complicated merge accounting logic 
> > in the core block layer? To me, it doesn't seem sensible.
> 
> Rip out the code if you like, then.  I really don't have time to
> work on this myself.  So if you do, by all means do whatever
> you think is appropriate.

So add signed-off line and forward it to Linus.

Signed-off-by: Mikulas Patocka <mpatocka@...hat.com>
---
 include/asm-sparc64/io.h |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

Index: linux-2.6.26-fast/include/asm-sparc64/io.h
===================================================================
--- linux-2.6.26-fast.orig/include/asm-sparc64/io.h	2008-07-15 23:29:39.000000000 +0200
+++ linux-2.6.26-fast/include/asm-sparc64/io.h	2008-07-15 23:33:41.000000000 +0200
@@ -16,7 +16,10 @@
 /* BIO layer definitions. */
 extern unsigned long kern_base, kern_size;
 #define page_to_phys(page)	(page_to_pfn(page) << PAGE_SHIFT)
-#define BIO_VMERGE_BOUNDARY	8192
+
+/* Don't declare that we are virtual-merge capable because Sparc64 IOMMU code
+   doesn't guarantee that the merge is always possible */
+#define BIO_VMERGE_BOUNDARY	0
 
 static inline u8 _inb(unsigned long addr)
 {
--
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