| Message ID | C21B8761-0447-45A6-B833-742E3B4C13DE@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 10/08/15 13:12, yalin wang wrote: > This change to use swab32(bitrev32()) to implement reverse_order() > function, have better performance on some platforms. Which platforms? Presuming you tested this, roughly how much better performance? If you didn't, how do you know it's faster? > Signed-off-by: yalin wang <yalin.wang2010@gmail.com> > --- > drivers/video/fbdev/riva/fbdev.c | 19 ++++++------------- > 1 file changed, 6 insertions(+), 13 deletions(-) > > diff --git a/drivers/video/fbdev/riva/fbdev.c b/drivers/video/fbdev/riva/fbdev.c > index f1ad274..4803901 100644 > --- a/drivers/video/fbdev/riva/fbdev.c > +++ b/drivers/video/fbdev/riva/fbdev.c > @@ -40,6 +40,7 @@ > #include <linux/init.h> > #include <linux/pci.h> > #include <linux/backlight.h> > +#include <linux/swab.h> > #include <linux/bitrev.h> > #ifdef CONFIG_PMAC_BACKLIGHT > #include <asm/machdep.h> > @@ -84,6 +85,7 @@ > #define SetBit(n) (1<<(n)) > #define Set8Bits(value) ((value)&0xff) > > +#define reverse_order(v) swab32(bitrev32(v)) > /* HW cursor parameters */ > #define MAX_CURS 32 > > @@ -451,15 +453,6 @@ static inline unsigned char MISCin(struct riva_par *par) > return (VGA_RD08(par->riva.PVIO, 0x3cc)); > } > > -static inline void reverse_order(u32 *l) I would suggest to do the work in the inline function, instead of a macro. And if you keep the function prototype the same, then the changes to each reverse_order call site are not needed. Tomi
> On Aug 20, 2015, at 19:02, Tomi Valkeinen <tomi.valkeinen@ti.com> wrote: > > > On 10/08/15 13:12, yalin wang wrote: >> This change to use swab32(bitrev32()) to implement reverse_order() >> function, have better performance on some platforms. > > Which platforms? Presuming you tested this, roughly how much better > performance? If you didn't, how do you know it's faster? i investigate on arm64 platforms: for (j = dsize; j--;) { tmp = data[k++]; tmp = reverse_order(tmp); NVDmaNext(par, tmp); bac: 110006a4 add w4, w21, #0x1 bb0: 5ac000a3 rbit w3, w5 if (dsize) { NVDmaStart(info, par, RECT_EXPAND_TWO_COLOR_DATA(0), dsize); for (j = dsize; j--;) { tmp = data[k++]; bb4: 110006d6 add w22, w22, #0x1 bb8: 5ac00861 rev w1, w3 tmp = reverse_order(tmp); NVDmaNext(par, tmp); bbc: b9041e64 str w4, [x19,#1052] bc0: 8b3548c2 add x2, x6, w21, uxtw #2 bc4: b9000041 str w1, [x2] this is the disassemble code after apply the patch, only need: rbit w3, w5 rev w1, w3 2 instruction to get the reverse_order() result, apparently after than the origianl macro code. > >> Signed-off-by: yalin wang <yalin.wang2010@gmail.com> >> --- >> drivers/video/fbdev/riva/fbdev.c | 19 ++++++------------- >> 1 file changed, 6 insertions(+), 13 deletions(-) >> >> diff --git a/drivers/video/fbdev/riva/fbdev.c b/drivers/video/fbdev/riva/fbdev.c >> index f1ad274..4803901 100644 >> --- a/drivers/video/fbdev/riva/fbdev.c >> +++ b/drivers/video/fbdev/riva/fbdev.c >> @@ -40,6 +40,7 @@ >> #include <linux/init.h> >> #include <linux/pci.h> >> #include <linux/backlight.h> >> +#include <linux/swab.h> >> #include <linux/bitrev.h> >> #ifdef CONFIG_PMAC_BACKLIGHT >> #include <asm/machdep.h> >> @@ -84,6 +85,7 @@ >> #define SetBit(n) (1<<(n)) >> #define Set8Bits(value) ((value)&0xff) >> >> +#define reverse_order(v) swab32(bitrev32(v)) >> /* HW cursor parameters */ >> #define MAX_CURS 32 >> >> @@ -451,15 +453,6 @@ static inline unsigned char MISCin(struct riva_par *par) >> return (VGA_RD08(par->riva.PVIO, 0x3cc)); >> } >> >> -static inline void reverse_order(u32 *l) > > I would suggest to do the work in the inline function, instead of a > macro. And if you keep the function prototype the same, then the changes > to each reverse_order call site are not needed. > ok, i will change to a inline function. -- To unsubscribe from this list: send the line "unsubscribe linux-fbdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 20/08/15 14:30, yalin wang wrote: > >> On Aug 20, 2015, at 19:02, Tomi Valkeinen <tomi.valkeinen@ti.com> wrote: >> >> >> On 10/08/15 13:12, yalin wang wrote: >>> This change to use swab32(bitrev32()) to implement reverse_order() >>> function, have better performance on some platforms. >> >> Which platforms? Presuming you tested this, roughly how much better >> performance? If you didn't, how do you know it's faster? > > i investigate on arm64 platforms: Ok. So is any arm64 platform actually using these devices? If these devices are mostly used by 32bit x86 platforms, optimizing them for arm64 doesn't make any sense. Possibly the patches are still good for x86 also, but that needs to be proven. Tomi
> On Aug 21, 2015, at 14:41, Tomi Valkeinen <tomi.valkeinen@ti.com> wrote: > > > > On 20/08/15 14:30, yalin wang wrote: >> >>> On Aug 20, 2015, at 19:02, Tomi Valkeinen <tomi.valkeinen@ti.com> wrote: >>> >>> >>> On 10/08/15 13:12, yalin wang wrote: >>>> This change to use swab32(bitrev32()) to implement reverse_order() >>>> function, have better performance on some platforms. >>> >>> Which platforms? Presuming you tested this, roughly how much better >>> performance? If you didn't, how do you know it's faster? >> >> i investigate on arm64 platforms: > > Ok. So is any arm64 platform actually using these devices? If these > devices are mostly used by 32bit x86 platforms, optimizing them for > arm64 doesn't make any sense. > > Possibly the patches are still good for x86 also, but that needs to be > proven. > not exactly, because x86_64 don’t have hardware instruction to do rbit OP, i compile by test : use the patch: use swab32(bitrev32()): 2775: 0f b6 d0 movzbl %al,%edx 2778: 0f b6 c4 movzbl %ah,%eax 277b: 0f b6 92 00 00 00 00 movzbl 0x0(%rdx),%edx 2782: 0f b6 80 00 00 00 00 movzbl 0x0(%rax),%eax 2789: c1 e2 08 shl $0x8,%edx 278c: 09 d0 or %edx,%eax 278e: 0f b6 d5 movzbl %ch,%edx 2791: 0f b6 c9 movzbl %cl,%ecx 2794: 0f b6 89 00 00 00 00 movzbl 0x0(%rcx),%ecx 279b: 0f b6 92 00 00 00 00 movzbl 0x0(%rdx),%edx 27a2: 0f b7 c0 movzwl %ax,%eax 27a5: c1 e1 08 shl $0x8,%ecx 27a8: 09 ca or %ecx,%edx 27aa: c1 e2 10 shl $0x10,%edx 27ad: 09 d0 or %edx,%eax 27af: 45 85 ff test %r15d,%r15d 27b2: 0f c8 bswap %eax 4 memory access instructions, without the patch: use do { \ - u8 *a = (u8 *)(l); \ - a[0] = bitrev8(a[0]); \ - a[1] = bitrev8(a[1]); \ - a[2] = bitrev8(a[2]); \ - a[3] = bitrev8(a[3]); \ -} while(0) 277b: 45 0f b6 80 00 00 00 movzbl 0x0(%r8),%r8d 2782: 00 2783: c1 ee 10 shr $0x10,%esi 2786: 89 f2 mov %esi,%edx 2788: 0f b6 f4 movzbl %ah,%esi 278b: c1 e8 18 shr $0x18,%eax 278e: 0f b6 d2 movzbl %dl,%edx 2791: 48 98 cltq 2793: 45 85 ed test %r13d,%r13d 2796: 0f b6 92 00 00 00 00 movzbl 0x0(%rdx),%edx 279d: 0f b6 80 00 00 00 00 movzbl 0x0(%rax),%eax 27a4: 44 88 85 54 ff ff ff mov %r8b,-0xac(%rbp) 27ab: 44 0f b6 86 00 00 00 movzbl 0x0(%rsi),%r8d 27b2: 00 27b3: 88 95 56 ff ff ff mov %dl,-0xaa(%rbp) 27b9: 88 85 57 ff ff ff mov %al,-0xa9(%rbp) 27bf: 44 88 85 55 ff ff ff mov %r8b,-0xab(%rbp) 6 memory access instructions, and generate more code that the patch . because the original code use byte access 4 times , i don’t think have better performance. :) Thanks -- To unsubscribe from this list: send the line "unsubscribe linux-fbdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 21/08/15 10:46, yalin wang wrote: >>> i investigate on arm64 platforms: >> >> Ok. So is any arm64 platform actually using these devices? If these >> devices are mostly used by 32bit x86 platforms, optimizing them for >> arm64 doesn't make any sense. >> >> Possibly the patches are still good for x86 also, but that needs to be >> proven. >> > not exactly, because x86_64 don’t have hardware instruction to do rbit OP, > i compile by test : For old drivers i386 may be more relevant than x86_64. So you don't have the actual HW? These kind of optimizations should have some real world measurements, not just compiling, looking at the assembly and guessing whether it's faster or not. Tomi
Hi, On Fri, Aug 21, 2015 at 11:01:41AM +0300, Tomi Valkeinen wrote: > >> Possibly the patches are still good for x86 also, but that needs to be > >> proven. > >> > > not exactly, because x86_64 don’t have hardware instruction to do rbit OP, > > i compile by test : > > For old drivers i386 may be more relevant than x86_64. It seems asm bit reversal is supported in Kernel on arm & arm64 only, not sure whether any other arch even provide asm bit reversal instruction. > These kind of optimizations should have some real world measurements, Not for this case, but once measured on ARM, iirc, a 32-bit asm bit reversal as compared to doing it in C was taking 1 cycle as opposed to ~225 cycles!, of course writing optimized C could have made it fare better, but still would reach no-way near asm bit reversal. Regards Afzal -- To unsubscribe from this list: send the line "unsubscribe linux-fbdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
> On Aug 22, 2015, at 15:53, Afzal Mohammed <afzal.mohd.ma@gmail.com> wrote: > > Hi, > > On Fri, Aug 21, 2015 at 11:01:41AM +0300, Tomi Valkeinen wrote: > >>>> Possibly the patches are still good for x86 also, but that needs to be >>>> proven. >>>> >>> not exactly, because x86_64 don’t have hardware instruction to do rbit OP, >>> i compile by test : >> >> For old drivers i386 may be more relevant than x86_64. > > It seems asm bit reversal is supported in Kernel on arm & arm64 only, > not sure whether any other arch even provide asm bit reversal > instruction. i only submit the bit reverse patch for arm / arm64 arch, i am not sure if there are some other arch also have hard ware bit reverse instructions, need arch maintainers to submit if their arch also have these hard ware instructions . :) > >> These kind of optimizations should have some real world measurements, > > Not for this case, but once measured on ARM, iirc, a 32-bit asm bit > reversal as compared to doing it in C was taking 1 cycle as opposed to > ~225 cycles!, of course writing optimized C could have made it fare > better, but still would reach no-way near asm bit reversal. > -- To unsubscribe from this list: send the line "unsubscribe linux-fbdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Hi, On Mon, Aug 24, 2015 at 04:31:13PM +0800, yalin wang wrote: > > i only submit the bit reverse patch for arm / arm64 arch, yes, saw later git blaming it on you :) > > Not for this case, but once measured on ARM, iirc, a 32-bit asm bit > > reversal as compared to doing it in C was taking 1 cycle as opposed to > > ~225 cycles!, of course writing optimized C could have made it fare > > better, but still would reach no-way near asm bit reversal. The above measurement was done not in Linux, rather on a baremetal code, but seeing the efficient Kernel C implementation, realized that the gain would not be that much, it would be good to know if there are measurements for Kernel bitreversal in C & asm (on supported arch) Regards afzal -- To unsubscribe from this list: send the line "unsubscribe linux-fbdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/drivers/video/fbdev/riva/fbdev.c b/drivers/video/fbdev/riva/fbdev.c index f1ad274..4803901 100644 --- a/drivers/video/fbdev/riva/fbdev.c +++ b/drivers/video/fbdev/riva/fbdev.c @@ -40,6 +40,7 @@ #include <linux/init.h> #include <linux/pci.h> #include <linux/backlight.h> +#include <linux/swab.h> #include <linux/bitrev.h> #ifdef CONFIG_PMAC_BACKLIGHT #include <asm/machdep.h> @@ -84,6 +85,7 @@ #define SetBit(n) (1<<(n)) #define Set8Bits(value) ((value)&0xff) +#define reverse_order(v) swab32(bitrev32(v)) /* HW cursor parameters */ #define MAX_CURS 32 @@ -451,15 +453,6 @@ static inline unsigned char MISCin(struct riva_par *par) return (VGA_RD08(par->riva.PVIO, 0x3cc)); } -static inline void reverse_order(u32 *l) -{ - u8 *a = (u8 *)l; - a[0] = bitrev8(a[0]); - a[1] = bitrev8(a[1]); - a[2] = bitrev8(a[2]); - a[3] = bitrev8(a[3]); -} - /* ------------------------------------------------------------------------- * * * cursor stuff @@ -497,8 +490,8 @@ static void rivafb_load_cursor_image(struct riva_par *par, u8 *data8, for (i = 0; i < h; i++) { b = *data++; - reverse_order(&b); - + b = reverse_order(b); + for (j = 0; j < w/2; j++) { tmp = 0; #if defined (__BIG_ENDIAN) @@ -1545,7 +1538,7 @@ static void rivafb_imageblit(struct fb_info *info, for (i = 0; i < 16; i++) { tmp = *((u32 *)cdat); cdat = (u8 *)((u32 *)cdat + 1); - reverse_order(&tmp); + tmp = reverse_order(tmp); NV_WR32(d, i*4, tmp); } size -= 16; @@ -1555,7 +1548,7 @@ static void rivafb_imageblit(struct fb_info *info, for (i = 0; i < size; i++) { tmp = *((u32 *) cdat); cdat = (u8 *)((u32 *)cdat + 1); - reverse_order(&tmp); + tmp = reverse_order(tmp); NV_WR32(d, i*4, tmp); } }
This change to use swab32(bitrev32()) to implement reverse_order() function, have better performance on some platforms. Signed-off-by: yalin wang <yalin.wang2010@gmail.com> --- drivers/video/fbdev/riva/fbdev.c | 19 ++++++------------- 1 file changed, 6 insertions(+), 13 deletions(-)