Re: [PATCH] i386: optimize memset of 6 and 8 bytes
From: Stephen Hemminger <[EMAIL PROTECTED]> Date: Fri, 17 Aug 2007 20:31:39 -0700 > On Fri, 17 Aug 2007 18:57:00 -0700 > Arjan van de Ven <[EMAIL PROTECTED]> wrote: > > > > > On Fri, 2007-08-17 at 18:54 -0700, Stephen Hemminger wrote: > > > On Fri, 17 Aug 2007 18:49:34 -0700 > > > Arjan van de Ven <[EMAIL PROTECTED]> wrote: > > > > > > > > > > > On Fri, 2007-08-17 at 16:50 -0700, Stephen Hemminger wrote: > > > > > Tne network code does memset for 6 and 8 byte values, that can easily > > > > > be optimized into simple assignments without string instructions. > > > > > > > > > > > > so... question. > > > > Why are we doing this by hand? Wouldn't gcc just generate this code in > > > > the first place (when using __builtin_memset)? I very much suspect it > > > > would (and if some version doesn't we really ought to get that > > > > fixed) > > > > > > i386 and x86_64 are not using __builtin_memset, as least from the > > > code that I see generated. > > > > .. maybe we should just fix it that way then? > > > There probably is history behind the decision, like gcc problems > on some old compiler version. Yes, but those reasons are very likely no longer true. In fact, just removing the memcpy macro altogether is the best thing to do. GCC will do inline memcpy when appropriate. Then put all of the rep; movsl; etc. code in an external assembler file and name the routine memcpy. The inlining is senseless even if it all gets optimized away into the bare necessary instructions. All the x86 registers get clobbered in most of those rep; movsl; code paths, so it's hardly going to be more expensive to extern the thing and it will make the kernel smaller to boot. Anyways the point is to make the real C symbol called by "memcpy" because that's what makes all the automatic gcc inline memcpy logic kick in. If you define the "memcpy" as a macro which calls differently named functions, you bypass all of that. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] i386: optimize memset of 6 and 8 bytes
On Fri, 17 Aug 2007 18:57:00 -0700 Arjan van de Ven <[EMAIL PROTECTED]> wrote: > > On Fri, 2007-08-17 at 18:54 -0700, Stephen Hemminger wrote: > > On Fri, 17 Aug 2007 18:49:34 -0700 > > Arjan van de Ven <[EMAIL PROTECTED]> wrote: > > > > > > > > On Fri, 2007-08-17 at 16:50 -0700, Stephen Hemminger wrote: > > > > Tne network code does memset for 6 and 8 byte values, that can easily > > > > be optimized into simple assignments without string instructions. > > > > > > > > > so... question. > > > Why are we doing this by hand? Wouldn't gcc just generate this code in > > > the first place (when using __builtin_memset)? I very much suspect it > > > would (and if some version doesn't we really ought to get that > > > fixed) > > > > i386 and x86_64 are not using __builtin_memset, as least from the > > code that I see generated. > > .. maybe we should just fix it that way then? > There probably is history behind the decision, like gcc problems on some old compiler version. -- Stephen Hemminger <[EMAIL PROTECTED]> - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] i386: optimize memset of 6 and 8 bytes
On Fri, 2007-08-17 at 18:54 -0700, Stephen Hemminger wrote: > On Fri, 17 Aug 2007 18:49:34 -0700 > Arjan van de Ven <[EMAIL PROTECTED]> wrote: > > > > > On Fri, 2007-08-17 at 16:50 -0700, Stephen Hemminger wrote: > > > Tne network code does memset for 6 and 8 byte values, that can easily > > > be optimized into simple assignments without string instructions. > > > > > > so... question. > > Why are we doing this by hand? Wouldn't gcc just generate this code in > > the first place (when using __builtin_memset)? I very much suspect it > > would (and if some version doesn't we really ought to get that > > fixed) > > i386 and x86_64 are not using __builtin_memset, as least from the > code that I see generated. .. maybe we should just fix it that way then? -- if you want to mail me at work (you don't), use arjan (at) linux.intel.com Test the interaction between Linux and your BIOS via http://www.linuxfirmwarekit.org - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] i386: optimize memset of 6 and 8 bytes
On Fri, 17 Aug 2007 18:49:34 -0700 Arjan van de Ven <[EMAIL PROTECTED]> wrote: > > On Fri, 2007-08-17 at 16:50 -0700, Stephen Hemminger wrote: > > Tne network code does memset for 6 and 8 byte values, that can easily > > be optimized into simple assignments without string instructions. > > > so... question. > Why are we doing this by hand? Wouldn't gcc just generate this code in > the first place (when using __builtin_memset)? I very much suspect it > would (and if some version doesn't we really ought to get that > fixed) i386 and x86_64 are not using __builtin_memset, as least from the code that I see generated. -- Stephen Hemminger <[EMAIL PROTECTED]> - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] i386: optimize memset of 6 and 8 bytes
On Fri, 2007-08-17 at 16:50 -0700, Stephen Hemminger wrote: > Tne network code does memset for 6 and 8 byte values, that can easily > be optimized into simple assignments without string instructions. so... question. Why are we doing this by hand? Wouldn't gcc just generate this code in the first place (when using __builtin_memset)? I very much suspect it would (and if some version doesn't we really ought to get that fixed) - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
[PATCH] i386: optimize memset of 6 and 8 bytes
Tne network code does memset for 6 and 8 byte values, that can easily be optimized into simple assignments without string instructions. Signed-off-by: Stephen Hemminger <[EMAIL PROTECTED]> --- a/include/asm-i386/string.h 2007-08-17 15:14:37.0 -0700 +++ b/include/asm-i386/string.h 2007-08-17 16:49:10.0 -0700 @@ -228,6 +228,14 @@ static __always_inline void * __constant case 4: *(unsigned long *)s = pattern; return s; + case 6: + *(unsigned long *)s = pattern; + *(2+(unsigned short *)s) = pattern; + return s; + case 8: + *(unsigned long *)s = pattern; + *(1+(unsigned long *)s) = pattern; + return s; } #define COMMON(x) \ __asm__ __volatile__( \ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
[PATCH] i386: optimize memset of 6 and 8 bytes
Tne network code does memset for 6 and 8 byte values, that can easily be optimized into simple assignments without string instructions. Signed-off-by: Stephen Hemminger [EMAIL PROTECTED] --- a/include/asm-i386/string.h 2007-08-17 15:14:37.0 -0700 +++ b/include/asm-i386/string.h 2007-08-17 16:49:10.0 -0700 @@ -228,6 +228,14 @@ static __always_inline void * __constant case 4: *(unsigned long *)s = pattern; return s; + case 6: + *(unsigned long *)s = pattern; + *(2+(unsigned short *)s) = pattern; + return s; + case 8: + *(unsigned long *)s = pattern; + *(1+(unsigned long *)s) = pattern; + return s; } #define COMMON(x) \ __asm__ __volatile__( \ - To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] i386: optimize memset of 6 and 8 bytes
On Fri, 2007-08-17 at 16:50 -0700, Stephen Hemminger wrote: Tne network code does memset for 6 and 8 byte values, that can easily be optimized into simple assignments without string instructions. so... question. Why are we doing this by hand? Wouldn't gcc just generate this code in the first place (when using __builtin_memset)? I very much suspect it would (and if some version doesn't we really ought to get that fixed) - To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] i386: optimize memset of 6 and 8 bytes
On Fri, 17 Aug 2007 18:49:34 -0700 Arjan van de Ven [EMAIL PROTECTED] wrote: On Fri, 2007-08-17 at 16:50 -0700, Stephen Hemminger wrote: Tne network code does memset for 6 and 8 byte values, that can easily be optimized into simple assignments without string instructions. so... question. Why are we doing this by hand? Wouldn't gcc just generate this code in the first place (when using __builtin_memset)? I very much suspect it would (and if some version doesn't we really ought to get that fixed) i386 and x86_64 are not using __builtin_memset, as least from the code that I see generated. -- Stephen Hemminger [EMAIL PROTECTED] - To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] i386: optimize memset of 6 and 8 bytes
On Fri, 2007-08-17 at 18:54 -0700, Stephen Hemminger wrote: On Fri, 17 Aug 2007 18:49:34 -0700 Arjan van de Ven [EMAIL PROTECTED] wrote: On Fri, 2007-08-17 at 16:50 -0700, Stephen Hemminger wrote: Tne network code does memset for 6 and 8 byte values, that can easily be optimized into simple assignments without string instructions. so... question. Why are we doing this by hand? Wouldn't gcc just generate this code in the first place (when using __builtin_memset)? I very much suspect it would (and if some version doesn't we really ought to get that fixed) i386 and x86_64 are not using __builtin_memset, as least from the code that I see generated. .. maybe we should just fix it that way then? -- if you want to mail me at work (you don't), use arjan (at) linux.intel.com Test the interaction between Linux and your BIOS via http://www.linuxfirmwarekit.org - To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] i386: optimize memset of 6 and 8 bytes
On Fri, 17 Aug 2007 18:57:00 -0700 Arjan van de Ven [EMAIL PROTECTED] wrote: On Fri, 2007-08-17 at 18:54 -0700, Stephen Hemminger wrote: On Fri, 17 Aug 2007 18:49:34 -0700 Arjan van de Ven [EMAIL PROTECTED] wrote: On Fri, 2007-08-17 at 16:50 -0700, Stephen Hemminger wrote: Tne network code does memset for 6 and 8 byte values, that can easily be optimized into simple assignments without string instructions. so... question. Why are we doing this by hand? Wouldn't gcc just generate this code in the first place (when using __builtin_memset)? I very much suspect it would (and if some version doesn't we really ought to get that fixed) i386 and x86_64 are not using __builtin_memset, as least from the code that I see generated. .. maybe we should just fix it that way then? There probably is history behind the decision, like gcc problems on some old compiler version. -- Stephen Hemminger [EMAIL PROTECTED] - To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] i386: optimize memset of 6 and 8 bytes
From: Stephen Hemminger [EMAIL PROTECTED] Date: Fri, 17 Aug 2007 20:31:39 -0700 On Fri, 17 Aug 2007 18:57:00 -0700 Arjan van de Ven [EMAIL PROTECTED] wrote: On Fri, 2007-08-17 at 18:54 -0700, Stephen Hemminger wrote: On Fri, 17 Aug 2007 18:49:34 -0700 Arjan van de Ven [EMAIL PROTECTED] wrote: On Fri, 2007-08-17 at 16:50 -0700, Stephen Hemminger wrote: Tne network code does memset for 6 and 8 byte values, that can easily be optimized into simple assignments without string instructions. so... question. Why are we doing this by hand? Wouldn't gcc just generate this code in the first place (when using __builtin_memset)? I very much suspect it would (and if some version doesn't we really ought to get that fixed) i386 and x86_64 are not using __builtin_memset, as least from the code that I see generated. .. maybe we should just fix it that way then? There probably is history behind the decision, like gcc problems on some old compiler version. Yes, but those reasons are very likely no longer true. In fact, just removing the memcpy macro altogether is the best thing to do. GCC will do inline memcpy when appropriate. Then put all of the rep; movsl; etc. code in an external assembler file and name the routine memcpy. The inlining is senseless even if it all gets optimized away into the bare necessary instructions. All the x86 registers get clobbered in most of those rep; movsl; code paths, so it's hardly going to be more expensive to extern the thing and it will make the kernel smaller to boot. Anyways the point is to make the real C symbol called by memcpy because that's what makes all the automatic gcc inline memcpy logic kick in. If you define the memcpy as a macro which calls differently named functions, you bypass all of that. - To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
