On Fri, 8 Feb 2013 22:16:47 -0500 Nicolas Pitre <n...@fluxnic.net> wrote:
> On Fri, 8 Feb 2013, Kim Phillips wrote: > > > On Fri, 8 Feb 2013 17:47:33 -0500 > > Nicolas Pitre <n...@fluxnic.net> wrote: > > > > > On Fri, 8 Feb 2013, Woodhouse, David wrote: > > > > > > > On Fri, 2013-02-08 at 15:04 -0500, Nicolas Pitre wrote: > > > > > On Fri, 8 Feb 2013, Woodhouse, David wrote: > > > > > > > > > > > On Thu, 2013-02-07 at 18:13 +0000, Russell King - ARM Linux wrote: > > > > > > > > > > > > > > However, the biggest reason not to use libgcc is that we want to > > > > > > > control > > > > > > > what gets used in the kernel - for example, no floating point, > > > > > > > and no > > > > > > > use of 64 x 64bit division. > > > > > > > > > > > > Which is all very sensible. But there's no particular reason we > > > > > > couldn't > > > > > > add a __bswap[sd]i2 to the kernel's version of libgcc if we wanted > > > > > > to. > > > > > > > > > > Absolutely. > > > > > > > > And then ARM can just set ARCH_USE_BUILTIN_BSWAP like other > > > > architectures do, right? > > > > > > If that turns out to be beneficial over what we have now, then yes. > > > I didn't read back the whole thread to form an opinion though. > > > > The diff below implements __bswap[sd]i2 in arch/arm/lib, and > > results in the following savings in vmlinux size: > > > > column 1: name of defconfig > > column 2: text+data+bss, linux-next-20130207 vanilla, gcc 4.6.3 > > column 3: text+data+bss, linux-next-20130207+below diff, gcc 4.6.3 > > column 4: col. 3 - col. 2 (ie., -ve numbers represent savings) > > > [...] > > imx_v6_v7_defconfig: 7672373 7667089 -5284 > > lart_defconfig: 2941150 2941054 -96 > > mxs_defconfig: 11091983 11095679 3696 > > The savings are good, with some impressive cases. However the > mxs_defconfig is completely the opposite and by far. Any idea? Unfortunately, I don't seem to be able to reproduce this anymore. Same linux-next, with three different compilers always produces smaller binaries: text data bss dec hex filename 5239363 280576 5569648 11089587 a936b3 linux-next-mxs-orig-gcc4.7/vmlinux 5239169 280556 5569648 11089373 a935dd linux-next-mxs-bswap-gcc4.7/vmlinux 5262223 280592 5569648 11112463 a9900f linux-next-mxs-orig-gcc4.6.3/vmlinux 5261909 280584 5569648 11112141 a98ecd linux-next-mxs-bswap-gcc4.6.3/vmlinux 5241379 280580 5569648 11091607 a93e97 linux-next-mxs-orig-gcc4.6ubuntu/vmlinux 5241189 280600 5569648 11091437 a93ded linux-next-mxs-bswap-gcc4.6ubuntu/vmlinux So I've since made a more consistent cross-build environment, using cross tools from Linaro [1,2] instead of via Ubuntu [3]. > > gcc 4.7.3 runs haven't been as good across the board as gcc 4.6.3, > > however: > > Not only that, but in many cases the results are wildly different given > the same config: > > > imx_v6_v7_defconfig: 7637605 7636935 -670 > > lart_defconfig: 2922550 2926600 4050 > > mxs_defconfig: 11071139 11070893 -246 > > The mxs_defconfig became much better while lart_defconfig regressed a > lot. > > > Haven't looked at why. > > Would be a good idea since this is rather weird and gcc could benefit > from your findings. The following is next-20130207 built with Linaro gcc 4.7.1 [1], and before and after the diff at the bottom of this email (and with normalized linux version string sizes): lart_defconfig: 2752106 120864 56444 2929414 2cb306 vmlinux lart_defconfig: 2756092 120864 56444 2933400 2cc298 vmlinux #builtin-bswap mxs_defconfig: 5229115 280572 5569648 11079335 a90ea7 vmlinux mxs_defconfig: 5228969 280552 5569648 11079169 a90e01 vmlinux #builtin-bswap imx_v6_v7_defconfig: 6935025 356172 360648 7651845 74c205 vmlinux imx_v6_v7_defconfig: 6934091 356180 360648 7650919 74be67 vmlinux #builtin-bswap so builtin-bswap improved mxs and imx_v6_v7 but in lart, it _added_ 3986 bytes to .text -> not good. Getting a closer look at lart, bloat-o-meter says the code actually shrunk: add/remove: 7/1 grow/shrink: 11/19 up/down: 298/-356 (-58) function old new delta inet_abc_len - 96 +96 __bswapdi2 - 52 +52 __bswapsi2 - 32 +32 icmp_unreach 472 492 +20 xfrm_selector_match 988 1000 +12 fib_table_insert 2176 2188 +12 __kstrtab___bswapsi2 - 11 +11 __kstrtab___bswapdi2 - 11 +11 __ksymtab___bswapsi2 - 8 +8 __ksymtab___bswapdi2 - 8 +8 vermagic 51 57 +6 linux_banner 230 236 +6 xfrm_replay_check_esn 320 324 +4 xfrm_replay_check_bmp 200 204 +4 xfrm_replay_check 152 156 +4 static.tcp_parse_aligned_timestamp 80 84 +4 fib_table_delete 708 712 +4 cookie_v4_check 1316 1320 +4 tcp_tso_segment 728 724 -4 tcp_options_write 724 720 -4 ip_rt_ioctl 1152 1148 -4 fib_trie_seq_show 724 720 -4 crc32_be 448 444 -4 xfrm_stateonly_find 640 632 -8 tcp_finish_connect 276 268 -8 static.tcp_v4_send_ack 480 472 -8 __xfrm_state_lookup 356 348 -8 __xfrm_state_bump_genids 436 428 -8 __find_acq_core 1256 1248 -8 cookie_v4_init_sequence 272 260 -12 __xfrm_state_insert 616 600 -16 sys_swapon 2500 2480 -20 xfrm_state_find 2420 2396 -24 xfrm_hash_resize 1620 1596 -24 fib_route_seq_show 560 536 -24 fib_table_dump 704 676 -28 devinet_ioctl 1856 1796 -60 static.inet_abc_len 80 - -80 Comparing System.maps, .rodata starts at the same address: c020a000 R __start_rodata c020a000 R __start_rodata #builtin-bswap however, changes including the __bswap[sd]i2 implementation pushes the .rodata section size just over the 4KiB alignment boundary specified in arm/kernel/vmlinux.lds: no builtin_bswap: c028ffc4 R __stop___modver c0290000 R __end_rodata c0290000 R __start___ex_table with builtin_bswap: c0290068 R __stop___modver c0291000 R __end_rodata c0291000 R __start___ex_table So, AFAICT, that's why we see a total increase in .text for lart, and, looking at both numbers being a little less than 4KiB, I suspect the same with whatever happened with mxs above. FYI, here are the same platforms with Linaro gcc 4.7.3 [2]: lart_defconfig: 2745218 120888 56444 2922550 2c9836 vmlinux lart_defconfig: 2749300 120888 56444 2926632 2ca828 vmlinux #builtin-bswap mxs_defconfig: 5220919 280572 5569648 11071139 a8eea3 vmlinux mxs_defconfig: 5220725 280552 5569648 11070925 a8edcd vmlinux #builtin-bswap imx_v6_v7_defconfig: 6920769 356188 360648 7637605 748a65 vmlinux imx_v6_v7_defconfig: 6920091 356196 360648 7636935 7487c7 vmlinux #builtin-bswap so lart is still mostly affected by the .rodata alignment: add/remove: 7/1 grow/shrink: 11/16 up/down: 330/-308 (22) function old new delta inet_abc_len - 96 +96 __bswapdi2 - 52 +52 fib_table_insert 2152 2196 +44 __bswapsi2 - 32 +32 icmp_unreach 472 492 +20 xfrm_selector_match 988 1000 +12 __kstrtab___bswapsi2 - 11 +11 __kstrtab___bswapdi2 - 11 +11 __ksymtab___bswapsi2 - 8 +8 __ksymtab___bswapdi2 - 8 +8 vermagic 51 57 +6 linux_banner 232 238 +6 xfrm_replay_check_esn 320 324 +4 xfrm_replay_check_bmp 200 204 +4 xfrm_replay_check 152 156 +4 static.tcp_parse_aligned_timestamp 80 84 +4 fib_table_delete 708 712 +4 cookie_v4_check 1316 1320 +4 tcp_options_write 724 720 -4 ip_rt_ioctl 1152 1148 -4 fib_trie_seq_show 724 720 -4 crc32_be 448 444 -4 xfrm_stateonly_find 640 632 -8 tcp_finish_connect 276 268 -8 static.tcp_v4_send_ack 480 472 -8 __xfrm_state_lookup 356 348 -8 __xfrm_state_bump_genids 436 428 -8 __find_acq_core 1252 1244 -8 cookie_v4_init_sequence 272 260 -12 __xfrm_state_insert 616 600 -16 xfrm_state_find 2420 2396 -24 xfrm_hash_resize 1620 1596 -24 fib_table_dump 704 676 -28 devinet_ioctl 1856 1796 -60 static.inet_abc_len 80 - -80 > > In any case, some questions I have are: > > > > (a) are the __bswap[sd]i2 implementations acceptable written in C, > > as in the diff? I don't speak ARM asm (yet at least). The > > generated code looks pretty optimal in both armv5 and 6+. > > It looks pretty nice indeed: > > __bswapsi2: > eor r2, r0, r0, ror #16 > mov r1, r2, lsr #8 > bic r3, r1, #65280 > eor r0, r3, r0, ror #8 > bx lr > > There is no way to do better than that. But that's true only if -Os is > _not_ used. With -Os we get the following output: > > __bswapsi2: > mov r3, r0, asl #24 > and r2, r0, #65280 > orr r3, r3, r0, lsr #24 > orr r3, r3, r2, asl #8 > and r0, r0, #16711680 > orr r0, r3, r0, lsr #8 > bx lr > > I really don't get why gcc thinks the above is shorter. I'm saving you > from pasting the __bswapdi2 result which is also way way worse. > That was with Linaro gcc v4.6.2. > > With Sourcery gcc v4.5.1 we get: > > __bswapsi2: > stmfd sp!, {r3, lr} > bl __bswapsi2 > ldmfd sp!, {r3, pc} > > This is indeed shorter, but much less useful. So you better enforce -O2 > for this file. And the nice thing with C code is that it is fully > optimized with the rev instruction when compiling for ARMv6+ if it is > ever used in that case. ok, so to avoid recursion, I've enforced a -O2 on bswapsdi2.o. > > (c) testing allyesconfigs is proving to be a pain - lots of > > breakeage - other than defconfig testing, is there any more I can do? > > The defconfigs provide wildly different results and that is a good > thing for further investigation. You may concentrate on a small > interesting sample such as those I kept above. > > With allyesconfig the good configs would cancel out the bad ones making > the bad ones invisible. ok, thanks for your comments, Nicolas. Here's the new diff: changes from last diff: - enforce -O2 for bswapsdi2.o - fix building out-of-source tree diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig index 4265a26..5e8b735 100644 --- a/arch/arm/Kconfig +++ b/arch/arm/Kconfig @@ -58,6 +58,7 @@ config ARM select CLONE_BACKWARDS select OLD_SIGSUSPEND3 select OLD_SIGACTION + select ARCH_USE_BUILTIN_BSWAP help The ARM series is a line of low-power-consumption RISC chip designs licensed by ARM Ltd and targeted at embedded applications and diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile index c9865f6..8ef97c4 100644 --- a/arch/arm/boot/compressed/Makefile +++ b/arch/arm/boot/compressed/Makefile @@ -111,12 +111,12 @@ endif targets := vmlinux vmlinux.lds \ piggy.$(suffix_y) piggy.$(suffix_y).o \ - lib1funcs.o lib1funcs.S ashldi3.o ashldi3.S \ + lib1funcs.o lib1funcs.S ashldi3.o ashldi3.S bswapsdi2.o \ font.o font.c head.o misc.o $(OBJS) # Make sure files are removed during clean extra-y += piggy.gzip piggy.lzo piggy.lzma piggy.xzkern \ - lib1funcs.S ashldi3.S $(libfdt) $(libfdt_hdrs) + lib1funcs.S ashldi3.S bswapsdi2.o $(libfdt) $(libfdt_hdrs) ifeq ($(CONFIG_FUNCTION_TRACER),y) ORIG_CFLAGS := $(KBUILD_CFLAGS) @@ -158,6 +158,12 @@ ashldi3 = $(obj)/ashldi3.o $(obj)/ashldi3.S: $(srctree)/arch/$(SRCARCH)/lib/ashldi3.S $(call cmd,shipped) +# For __bswapsi2, __bswapdi2 +bswapsdi2 = $(obj)/bswapsdi2.o + +$(obj)/bswapsdi2.o: $(obj)/../../../../arch/$(SRCARCH)/lib/bswapsdi2.o + $(call cmd,shipped) + # We need to prevent any GOTOFF relocs being used with references # to symbols in the .bss section since we cannot relocate them # independently from the rest at run time. This can be achieved by @@ -179,7 +185,8 @@ if [ $(words $(ZRELADDR)) -gt 1 -a "$(CONFIG_AUTO_ZRELADDR)" = "" ]; then \ fi $(obj)/vmlinux: $(obj)/vmlinux.lds $(obj)/$(HEAD) $(obj)/piggy.$(suffix_y).o \ - $(addprefix $(obj)/, $(OBJS)) $(lib1funcs) $(ashldi3) FORCE + $(addprefix $(obj)/, $(OBJS)) $(lib1funcs) $(ashldi3) \ + $(bswapsdi2) FORCE @$(check_for_multiple_zreladdr) $(call if_changed,ld) @$(check_for_bad_syms) diff --git a/arch/arm/kernel/armksyms.c b/arch/arm/kernel/armksyms.c index 60d3b73..ba578f7 100644 --- a/arch/arm/kernel/armksyms.c +++ b/arch/arm/kernel/armksyms.c @@ -35,6 +35,8 @@ extern void __ucmpdi2(void); extern void __udivsi3(void); extern void __umodsi3(void); extern void __do_div64(void); +extern void __bswapsi2(void); +extern void __bswapdi2(void); extern void __aeabi_idiv(void); extern void __aeabi_idivmod(void); @@ -114,6 +116,8 @@ EXPORT_SYMBOL(__ucmpdi2); EXPORT_SYMBOL(__udivsi3); EXPORT_SYMBOL(__umodsi3); EXPORT_SYMBOL(__do_div64); +EXPORT_SYMBOL(__bswapsi2); +EXPORT_SYMBOL(__bswapdi2); #ifdef CONFIG_AEABI EXPORT_SYMBOL(__aeabi_idiv); diff --git a/arch/arm/lib/Makefile b/arch/arm/lib/Makefile index af72969..dbee639 100644 --- a/arch/arm/lib/Makefile +++ b/arch/arm/lib/Makefile @@ -13,7 +13,7 @@ lib-y := backtrace.o changebit.o csumipv6.o csumpartial.o \ ashldi3.o ashrdi3.o lshrdi3.o muldi3.o \ ucmpdi2.o lib1funcs.o div64.o \ io-readsb.o io-writesb.o io-readsl.o io-writesl.o \ - call_with_stack.o + call_with_stack.o bswapsdi2.o mmu-y := clear_user.o copy_page.o getuser.o putuser.o @@ -45,3 +45,5 @@ lib-$(CONFIG_ARCH_SHARK) += io-shark.o $(obj)/csumpartialcopy.o: $(obj)/csumpartialcopygeneric.S $(obj)/csumpartialcopyuser.o: $(obj)/csumpartialcopygeneric.S + +CFLAGS_bswapsdi2.o = -O2 diff --git a/arch/arm/lib/bswapsdi2.c b/arch/arm/lib/bswapsdi2.c new file mode 100644 index 0000000..1923b2f --- /dev/null +++ b/arch/arm/lib/bswapsdi2.c @@ -0,0 +1,19 @@ +unsigned int __bswapsi2(unsigned int x) +{ + return ((x & 0x000000ffUL) << 24) | + ((x & 0x0000ff00UL) << 8) | + ((x & 0x00ff0000UL) >> 8) | + ((x & 0xff000000UL) >> 24); +} + +unsigned long long __bswapdi2(unsigned long long x) +{ + return ((x & 0x00000000000000ffULL) << 56) | + ((x & 0x000000000000ff00ULL) << 40) | + ((x & 0x0000000000ff0000ULL) << 24) | + ((x & 0x00000000ff000000ULL) << 8) | + ((x & 0x000000ff00000000ULL) >> 8) | + ((x & 0x0000ff0000000000ULL) >> 24) | + ((x & 0x00ff000000000000ULL) >> 40) | + ((x & 0xff00000000000000ULL) >> 56); +} Thanks, Kim [1] arm-linux-gnueabihf-gcc (crosstool-NG linaro-1.13.1-2012.06-20120625 - Linaro GCC 2012.06) 4.7.1 20120531 (prerelease) [2] arm-linux-gnueabihf-gcc (crosstool-NG linaro-1.13.1-4.7-2013.01-20130125 - Linaro GCC 2013.01) 4.7.3 20130102 (prerelease) [3] gcc version 4.6.3 20120624 (prerelease) (Ubuntu/Linaro 4.6.3-8ubuntu1) (deb http://mirrors.us.kernel.org/ubuntu/ precise main universe) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/