On Wed, 18 Jul 2012, Konstantin Belousov wrote:
On Wed, Jul 18, 2012 at 02:36:16PM +1000, Bruce Evans wrote:
On Wed, 18 Jul 2012, Konstantin Belousov wrote:
...
The curpcb access shall be spelled as PCPU_GET(curpcb). Please note that
compiler is not allowed to cache the accesses, since there is __asm
__volatile expression to indirect through %gs-prefixed read.
Fix curpcb then. curthread was de-pessimized to use __pure2 and to not
use __volatile. I could never this to work to cache curthread when I
ried it, but it apparently works in -current.
..
curpcb() could be implemented like this for amd64 only:
Similarly for i386?
diff --git a/sys/amd64/include/pcb.h b/sys/amd64/include/pcb.h
index 22cbbe2..3417c52 100644
--- a/sys/amd64/include/pcb.h
+++ b/sys/amd64/include/pcb.h
@@ -144,6 +144,17 @@ void makectx(struct trapframe *, struct pcb *);
int savectx(struct pcb *) __returns_twice;
void resumectx(struct pcb *);
+static __inline __pure2 struct pcb *
+__curpcb(void)
+{
+ struct pcb *pcb;
+
+ __asm("movq %%gs:%1,%0" : "=r" (pcb)
+ : "i" (offsetof(struct pcpu, pc_curpcb)));
pc_curpcb is only a pointer, so there is no need for pcb.h to be used
(any more than proc.h is neaded for __curthread()).
I think this can go in machine/pcpu.h next to __curthread(). Or
machine/cpuinfo can provide the an alternative to PCPU_GET() without
__volatile and sys/pcpu.h can do this.
__curthread() avoids a dependency on sys/pcpu.h by hard-coding the
offset of pc_curthread as 0. This hack seems to be unnecessary,
Including machine/pcpu.h without going through sys/pcpu.h should be an
error. This error is only in a few low tier files:
- i386/xen/pcpu.h: this bogusly includes machine/pcpu.h after already
including sys/cpu.h
- mips/cavium/octeon_machdep.c
- mips/cavium/uart_dev_oct16550.c
- powerpc/include/platform.h
- xen/evtchn.h. xen code is horrible. In i386/include/xen/xen_os.h,
as part of this file's namespace pollution, it claims to include
sys/time.h for pcpu.h. But actually sys/time.h only provides moderate
namespace pollution that doesn't include pcpu.h. It is another style
bug to include sys/time.h directly. sys/time.h is standard namespace
pollution in sys/param.h in the _KERNEL case.
So amd64 can apparently safely put this function in machine/pcpu.h.
i386 might have to untangle the xen pollution. Other arches aren't
directly affected, since they don't have npx. I wondered if they
even had curpcb (if not then pc_curpcb should be in the MD fields).
Grep shows that they have considerable variation and messes. At
lease ia64 doesn't use the "MI" pc_curpcb. There is similar variation
and messes for pcpup.
+ return (pcb);
+}
+#define curpcb (__curpcb())
+
#endif
#endif /* _AMD64_PCB_H_ */
diff --git a/sys/sys/user.h b/sys/sys/user.h
index accb7c3..ab1c7a7 100644
--- a/sys/sys/user.h
+++ b/sys/sys/user.h
@@ -35,6 +35,7 @@
#ifndef _SYS_USER_H_
#define _SYS_USER_H_
+#include <sys/pcpu.h>
Too much namespace pollution for me.
#include <machine/pcb.h>
Putting the definiton in machine/pcpu.h should avoid changing the
prerequistes for machine/pcb.h.
#ifndef _KERNEL
/* stuff that *used* to be included by user.h, or is now needed */
Please note the location in pcb.h an not in machine/pcpu.h, where it
cannot work for technical reasons (struct pcpu is not defined yet).
Not applicable -- see above.
This should be committed separetely, together with the pass over amd64/
to convert PCPU_GET(curpcb) into curpcb().
Do you agree with committing the PR fix as is and adding the curpcb() later ?
And removing fnclex() later (it seems I convinced enough for its removal).
OK.
Bruce
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