Messages in this thread | | | Date | Thu, 31 Jul 2003 16:07:58 +0100 | From | Jamie Lokier <> | Subject | Re: TSCs are a no-no on i386 |
| |
Willy Tarreau wrote: > The other problem lies with the lock : > When a 486 executes "LOCK ; CMPXCHG", it locks the bus during the whole cmpxchg > instruction. If a 386 executes the same code, it will get an exception which > will be caught by the emulator. I don't see how we can do such an atomic > operation while holding a lock. At best, we would think about a global memory > based shared lock during the operation (eg: int bus_lock;), but it's not > implemented at the moment, and will only be compatible with processors sharing > the same code. Add-on processors, such as co-processors, transputer cards, or > DSPs, will know nothing about such a lock emulation. And it would result in > even poorer performance of course !
Of course this is not a problem when "lock;cmpxchg" is used only for thread synchronisation on uniprocessor 386s... The lock prefix is irrelevant then.
Perhaps the emulation should refuse to pretend to work on an SMP 386 :)
-- Jamie - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |