> On Monday 08 June 2009 21:35:05 matthieu castet wrote: >> Michael Buesch wrote: >> > On Sunday 07 June 2009 11:28:50 matthieu castet wrote: >> >> Hi, >> >> >> >> I wonder with openwrt for bcm47xx is not build with "-msoft-float". >> >> The cpu doesn't have fpu and the current floating code get emulated by the >> >> kernel emulator instead of using the gcc emulation support (that is >> >> cheaper >> >> because there is no kernel trap). >> > >> > Well, I guess on a typical bcm47xx setup there's hardly any application >> > that uses >> > floating point math. >> note that dropbear seems to use some, but that not critical. >> >> > Does -msoft-float increase the binary/image size? If so, I'd >> > vote for _not_ adding -msoft-float. If it doesn't make a size difference, >> > we should >> > probably add it. >> > >> That shouldn't increase size of application that don't use float. >> I did a quick test with dropbear that contain very few float. >> Here are the results (sfloat means -msoft-float, sgcc mean -shared-libgcc) >> >> >> $size /tmp/dropbear* >> text data bss dec hex filename >> 226924 4252 1744 232920 38dd8 /tmp/dropbear >> 234719 4328 1744 240791 3ac97 /tmp/dropbear_sfloat >> 220781 4192 1744 226717 3759d /tmp/dropbear_sfloat_sgcc >> 219956 4152 1744 225852 3723c /tmp/dropbear_sgcc >> >> As you can see with a static libgcc the size of the softfloat binary >> increase (8k) because all float emulation code is duplicated in the binary. >> With a shared libgcc the softfloat binary is smaller, the increase size >> is less than 1k. >> >> I don't know the impact for whole binary. I should try to build a >> typical bcm47xx setup and see the impact. > > Ok. It still smells like we're trying to solve a problem that does not exist. > Is the performance of any app increased in real life?
FWIW, I'd be interested to get faster floating point operations in an app I wrote that runs on openwrt. I'm running kernel 2.4 on brcm53xx -- if that's a relevant testing platform for this question, I could try some tests to see how much it speeds things up. If yes, then please let me know how to use the different floating point library (do I need to build a new toolchain? or is it an option in make menuconfig?) Dan _______________________________________________ openwrt-devel mailing list openwrt-devel@lists.openwrt.org https://lists.openwrt.org/mailman/listinfo/openwrt-devel
