Steven Seeger wrote:
> It is being called a lot. Running my test with the break in both loops
> yields approximately 60 calls to it. Half of those are called even
> before i387.c's init_fpu().
For the records: we found a solution to this FPU issue. The issue was
two-fold:
- when xenomai was preempting some linux kernel code which has called
kernel_fpu_begin, it was saving the current FPU context over the current
thread user-space FPU backup area, erasing its value previously saved by
kernel_fpu_begin();
- xenomai could preempt the linux kernel anywhere within the
kernel_fpu_begin function, which caused it to observe an incoherent
state (namely incoherent values of
current_thread_info()->status & TS_USEDFPU and TS bit in CR0).
These issues were easy to observe on Geode, because Linux on these
processors use MMX, thus kernel_fpu_begin routinely.
So, the following patch should be integrated into the I-pipe patch:
diff --git a/include/asm-x86/i387.h b/include/asm-x86/i387.h
index 56d00e3..e850fa1 100644
--- a/include/asm-x86/i387.h
+++ b/include/asm-x86/i387.h
@@ -222,11 +222,14 @@ static inline void __clear_fpu(struct task_struct
*tsk)
static inline void kernel_fpu_begin(void)
{
struct thread_info *me = current_thread_info();
+ unsigned long flags;
preempt_disable();
+ local_irq_save_hw_cond(flags);
if (me->status & TS_USEDFPU)
__save_init_fpu(me->task);
else
clts();
+ local_irq_restore_hw_cond(flags);
}
static inline void kernel_fpu_end(void)
And the following patch should be applied to Xenomai:
Index: include/asm-x86/bits/pod_32.h
===================================================================
--- include/asm-x86/bits/pod_32.h (revision 4572)
+++ include/asm-x86/bits/pod_32.h (working copy)
@@ -63,7 +63,12 @@ static inline void xnarch_leave_root(xna
rootcb->ts_usedfpu = wrap_test_fpu_used(current) != 0;
rootcb->cr0_ts = (read_cr0() & 8) != 0;
/* So that xnarch_save_fpu() will operate on the right FPU area. */
- rootcb->fpup = x86_fpustate_ptr(&rootcb->user_task->thread);
+ if (rootcb->cr0_ts || rootcb->ts_usedfpu)
+ rootcb->fpup = x86_fpustate_ptr(&rootcb->user_task->thread);
+ else
+ /* the kernel is currently using fpu in kernel-space, do not
+ clobber the user-space fpu backup area. */
+ rootcb->fpup = &rootcb->i387;
}
#define xnarch_enter_root(rootcb) do { } while(0)
--
Gilles.
_______________________________________________
Adeos-main mailing list
[email protected]
https://mail.gna.org/listinfo/adeos-main
