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From: Borislav Petkov <bp@alien8.de>
To: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>,
	linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
	Ross Zwisler <ross.zwisler@linux.intel.com>,
	"H . Peter Anvin" <hpa@linux.intel.com>
Subject: Re: [PATCH] x86: Add an explicit barrier() to clflushopt()
Date: Mon, 19 Oct 2015 12:16:12 +0200	[thread overview]
Message-ID: <20151019101612.GA20341@pd.tnic> (raw)
In-Reply-To: <1445248735-11915-1-git-send-email-chris@chris-wilson.co.uk>

On Mon, Oct 19, 2015 at 10:58:55AM +0100, Chris Wilson wrote:
> During testing we observed that the last cacheline was not being flushed
> from a
> 
> 	mb()
> 	for (addr = addr & -clflush_size; addr < end; addr += clflush_size)
> 		clflushopt();
> 	mb()
> 
> loop (where the initial addr and end were not cacheline aligned).
> 
> Changing the loop from addr < end to addr <= end, or replacing the
> clflushopt() with clflush() both fixed the testcase. Hinting that GCC
> was miscompling the assembly within the loop and specifically the
> alternative within clflushopt() was confusing the loop optimizer.
> 
> Adding a barrier() into clflushopt() is enough for GCC to dtrt, but
> solving why GCC is not seeing the constraints from the alternative_io()
> would be smarter...

Hmm, would something like adding the memory clobber to the
alternative_io() definition work?

---
diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h
index 7bfc85bbb8ff..d923e5dacdb1 100644
--- a/arch/x86/include/asm/alternative.h
+++ b/arch/x86/include/asm/alternative.h
@@ -207,7 +207,7 @@ static inline int alternatives_text_reserved(void *start, void *end)
 /* Like alternative_input, but with a single output argument */
 #define alternative_io(oldinstr, newinstr, feature, output, input...)	\
 	asm volatile (ALTERNATIVE(oldinstr, newinstr, feature)		\
-		: output : "i" (0), ## input)
+		: output : "i" (0), ## input : "memory")
 
 /* Like alternative_io, but for replacing a direct call with another one. */
 #define alternative_call(oldfunc, newfunc, feature, output, input...)	\

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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WARNING: multiple messages have this Message-ID (diff)
From: Borislav Petkov <bp@alien8.de>
To: Chris Wilson <chris@chris-wilson.co.uk>
Cc: linux-kernel@vger.kernel.org,
	Ross Zwisler <ross.zwisler@linux.intel.com>,
	"H . Peter Anvin" <hpa@linux.intel.com>,
	Imre Deak <imre.deak@intel.com>,
	Daniel Vetter <daniel.vetter@ffwll.ch>,
	dri-devel@lists.freedesktop.org
Subject: Re: [PATCH] x86: Add an explicit barrier() to clflushopt()
Date: Mon, 19 Oct 2015 12:16:12 +0200	[thread overview]
Message-ID: <20151019101612.GA20341@pd.tnic> (raw)
In-Reply-To: <1445248735-11915-1-git-send-email-chris@chris-wilson.co.uk>

On Mon, Oct 19, 2015 at 10:58:55AM +0100, Chris Wilson wrote:
> During testing we observed that the last cacheline was not being flushed
> from a
> 
> 	mb()
> 	for (addr = addr & -clflush_size; addr < end; addr += clflush_size)
> 		clflushopt();
> 	mb()
> 
> loop (where the initial addr and end were not cacheline aligned).
> 
> Changing the loop from addr < end to addr <= end, or replacing the
> clflushopt() with clflush() both fixed the testcase. Hinting that GCC
> was miscompling the assembly within the loop and specifically the
> alternative within clflushopt() was confusing the loop optimizer.
> 
> Adding a barrier() into clflushopt() is enough for GCC to dtrt, but
> solving why GCC is not seeing the constraints from the alternative_io()
> would be smarter...

Hmm, would something like adding the memory clobber to the
alternative_io() definition work?

---
diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h
index 7bfc85bbb8ff..d923e5dacdb1 100644
--- a/arch/x86/include/asm/alternative.h
+++ b/arch/x86/include/asm/alternative.h
@@ -207,7 +207,7 @@ static inline int alternatives_text_reserved(void *start, void *end)
 /* Like alternative_input, but with a single output argument */
 #define alternative_io(oldinstr, newinstr, feature, output, input...)	\
 	asm volatile (ALTERNATIVE(oldinstr, newinstr, feature)		\
-		: output : "i" (0), ## input)
+		: output : "i" (0), ## input : "memory")
 
 /* Like alternative_io, but for replacing a direct call with another one. */
 #define alternative_call(oldfunc, newfunc, feature, output, input...)	\

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.

  reply	other threads:[~2015-10-19 10:16 UTC|newest]

Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-10-19  9:58 [PATCH] x86: Add an explicit barrier() to clflushopt() Chris Wilson
2015-10-19  9:58 ` Chris Wilson
2015-10-19 10:16 ` Borislav Petkov [this message]
2015-10-19 10:16   ` Borislav Petkov
2015-10-19 11:05   ` Chris Wilson
2015-10-19 11:05     ` Chris Wilson
2015-10-19 11:25     ` Borislav Petkov
2015-10-19 11:25       ` Borislav Petkov
2015-10-19 18:29 ` Ross Zwisler
2016-01-07 10:16 ` Chris Wilson
2016-01-07 10:16   ` Chris Wilson
2016-01-07 17:55   ` Andy Lutomirski
2016-01-07 17:55     ` Andy Lutomirski
2016-01-07 19:44     ` Chris Wilson
2016-01-07 19:44       ` Chris Wilson
2016-01-07 21:05       ` H. Peter Anvin
2016-01-07 21:54         ` Chris Wilson
2016-01-07 21:54           ` Chris Wilson
2016-01-07 22:29           ` H. Peter Anvin
2016-01-07 22:29             ` H. Peter Anvin
2016-01-07 22:32             ` H. Peter Anvin
2016-01-07 22:32               ` H. Peter Anvin
2016-01-09  5:55               ` H. Peter Anvin
2016-01-09  8:01               ` Chris Wilson
2016-01-09  8:01                 ` Chris Wilson
2016-01-09 22:36                 ` Andy Lutomirski
2016-01-09 22:36                   ` Andy Lutomirski
2016-01-11 11:28                   ` Chris Wilson
2016-01-11 11:28                     ` Chris Wilson
2016-01-11 20:11                     ` Linus Torvalds
2016-01-11 20:11                       ` Linus Torvalds
2016-01-11 21:05                       ` Chris Wilson
2016-01-11 21:05                         ` Chris Wilson
2016-01-12 16:37                         ` Chris Wilson
2016-01-12 16:37                           ` Chris Wilson
2016-01-12 17:05                           ` Linus Torvalds
2016-01-12 17:05                             ` Linus Torvalds
2016-01-12 21:13                             ` Chris Wilson
2016-01-12 21:13                               ` Chris Wilson
2016-01-12 22:07                               ` Linus Torvalds
2016-01-12 22:07                                 ` Linus Torvalds
2016-01-13  0:55                                 ` Chris Wilson
2016-01-13  0:55                                   ` Chris Wilson
2016-01-13  2:06                                   ` Linus Torvalds
2016-01-13  2:06                                     ` Linus Torvalds
2016-01-13  2:42                                     ` Andy Lutomirski
2016-01-13  2:42                                       ` Andy Lutomirski
2016-01-13  4:39                                       ` Linus Torvalds
2016-01-13  4:39                                         ` Linus Torvalds
2016-01-13 12:34                                     ` Chris Wilson
2016-01-13 12:34                                       ` Chris Wilson
2016-01-13 18:45                                       ` Linus Torvalds
2016-01-13 18:45                                         ` Linus Torvalds
2016-01-12 17:17                     ` H. Peter Anvin
2016-01-12 17:17                       ` H. Peter Anvin

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