H. Peter Anvin wrote:
>>> Ummm...last I knew, fxrstor is *expensive*. The fninit/xor regs
>>> setup is likely *very* much faster. Someone should check this
>>> before we sacrifice 100 cycles needlessly or something.
>>
>> most probably yes, fxrestor needs to read ram, pxor also takes
>> some icache and bytecode ram but it sounds like it will be faster.
>>
>> Maybe we could also interleave the pxor with the xorps, since they
>> uses different parts of the cpu, Honza?
>>
>
>
> You almost certainly should. The reason I suggested FXRSTOR is that
> it would initialize the entire FPU, including any state that future
> processors may add, thus reducing the likelihood of any funnies in
> the future.
Here's a patch to do just that. It initializes the saved state in the
task struct and falls through to restore_fpu().
--Brian Gerst
diff -urN linux-2.5.8/arch/i386/kernel/i387.c linux/arch/i386/kernel/i387.c --- linux-2.5.8/arch/i386/kernel/i387.c Thu Mar 7 21:18:32 2002 +++ linux/arch/i386/kernel/i387.c Fri Apr 19 18:23:53 2002 @@ -31,13 +31,20 @@ * value at reset if we support XMM instructions and then * remeber the current task has used the FPU. */ -void init_fpu(void) +void init_fpu(struct task_struct *tsk) { - __asm__("fninit"); - if ( cpu_has_xmm ) - load_mxcsr(0x1f80); - - current->used_math = 1; + if ( cpu_has_xmm ) { + memset(&tsk->thread.i387.fxsave, 0, sizeof(struct i387_fxsave_struct)); + tsk->thread.i387.fxsave.cwd = 0x37f; + tsk->thread.i387.fxsave.mxcsr = 0x1f80; + } else { + memset(&tsk->thread.i387.fsave, 0, sizeof(struct i387_fsave_struct)); + tsk->thread.i387.fsave.cwd = 0xffff037f; + tsk->thread.i387.fsave.swd = 0xffff0000; + tsk->thread.i387.fsave.twd = 0xffffffff; + tsk->thread.i387.fsave.fos = 0xffff0000; + } + tsk->used_math = 1; } /* diff -urN linux-2.5.8/arch/i386/kernel/traps.c linux/arch/i386/kernel/traps.c --- linux-2.5.8/arch/i386/kernel/traps.c Sun Apr 14 23:48:18 2002 +++ linux/arch/i386/kernel/traps.c Fri Apr 19 18:22:12 2002 @@ -757,13 +757,12 @@ */ asmlinkage void math_state_restore(struct pt_regs regs) { + struct task_struct *tsk = current; clts(); /* Allow maths ops (or we recurse) */ - if (current->used_math) { - restore_fpu(current); - } else { - init_fpu(); - } + if (!tsk->used_math) + init_fpu(tsk); + restore_fpu(tsk); set_thread_flag(TIF_USEDFPU); /* So we fnsave on switch_to() */ } diff -urN linux-2.5.8/include/asm-i386/i387.h linux/include/asm-i386/i387.h --- linux-2.5.8/include/asm-i386/i387.h Fri Apr 19 18:44:48 2002 +++ linux/include/asm-i386/i387.h Fri Apr 19 18:46:12 2002 @@ -17,7 +17,7 @@ #include <asm/sigcontext.h> #include <asm/user.h> -extern void init_fpu(void); +extern void init_fpu(struct task_struct *); /* * FPU lazy state save handling... */
- 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/
This archive was generated by hypermail 2b29 : Tue Apr 23 2002 - 22:00:25 EST