Ralf Baechle wrote: > On Thu, Jul 04, 2002 at 10:47:41AM +0200, Kevin D. Kissell wrote: > > >>The R5900 kernel for the Playstation 2 does not use system >>calls. It uses a memory-mapped pseudo-device hack that >>the guys at Sony came up with, which is much faster. We >>at MIPS came up with an even faster hack which uses >>the destruction of a "k" register value, but which requires >>the branch-likely instruction and thus only workson >>MIPS II CPUs and above (R39xxx, R4xxx, R5xxx, >>but not the classic R3K). See my message >>"Re: patches for test-and-set without ll/sc" of January 22. >> >>I consider it to be very important for MIPS/Linux >>that the embedded/workstation kernel and libraries >>merge with the Playstation 2 "consumer" Linux, and >>I don't think that will happen if we try to push the >>PS2 people to use something far less efficient than >>what they already have. "Entia non sunt multiplicanda >>praeter necessitatem", as a wise old guy once said, >>but could we not consider a MIPS/Linux universe >>where R3000 binaries use system calls, non-LL/SC >>MIPSII+ binaries use k-register destruction, real, >>manly, MIPS binaries use LL/SC instructions, and >>where the MIPS/Linux kernel (a) supports an appropriate >>system call, (b) makes a contract with userland to >>destroy k-regs predictably, and (c) contains the >>emulation logic for LL/SC? That should give us >>full cross-platform binary compatibility, with optimal >>performance on each platform when an appropriately >>configured set of libraries and tools is installed. >> > > No, Sony's ABI isn't MP proof and will break silently on MP systems. As > such I can't consider it anything else but a hack. sysmips(MIPS_ATOMIC_SET, > ...) and ll/sc however are MP proof. > sysmips(MIPS_ATOMIC_SET, ...) as it is is not MP-safe. Two processors can set the variable at the same time since no spinlock is used to protect the access. This is also a problem when I was writing preemptiable kernel patch. Jun
