Author: marcel
Date: Tue Feb 12 17:38:35 2013
New Revision: 246715
URL: http://svnweb.freebsd.org/changeset/base/246715
Log:
Eliminate the PC_CURTHREAD symbol and load the current thread's
thread structure pointer atomically from r13 (the pcpu pointer)
for the current CPU/core.
Add a CTASSERT in machdep.c to make sure that pc_curthread is in
fact the first field in struct pcpu.
The only non-atomic operations left were those related to process-
space operations, such as casuword, subyte, suword16, fubyte,
fuword16, copyin, copyout and their variations.
The casuword function has been re-structured more complete than
the others. This way we have an example of a better bundling
without introducing a lot of risk when we get it wrong. The
other functions can be rebundled in separate commits and with
the appropriate testing.
Modified:
head/sys/ia64/ia64/genassym.c
head/sys/ia64/ia64/machdep.c
head/sys/ia64/ia64/support.S
Modified: head/sys/ia64/ia64/genassym.c
==============================================================================
--- head/sys/ia64/ia64/genassym.c Tue Feb 12 17:24:41 2013
(r246714)
+++ head/sys/ia64/ia64/genassym.c Tue Feb 12 17:38:35 2013
(r246715)
@@ -96,7 +96,6 @@ ASSYM(PAGE_SHIFT, PAGE_SHIFT);
ASSYM(PAGE_SIZE, PAGE_SIZE);
ASSYM(PC_CURRENT_PMAP, offsetof(struct pcpu, pc_md.current_pmap));
-ASSYM(PC_CURTHREAD, offsetof(struct pcpu, pc_curthread));
ASSYM(PC_IDLETHREAD, offsetof(struct pcpu, pc_idlethread));
ASSYM(PCB_CURRENT_PMAP, offsetof(struct pcb, pcb_current_pmap));
Modified: head/sys/ia64/ia64/machdep.c
==============================================================================
--- head/sys/ia64/ia64/machdep.c Tue Feb 12 17:24:41 2013
(r246714)
+++ head/sys/ia64/ia64/machdep.c Tue Feb 12 17:38:35 2013
(r246715)
@@ -98,6 +98,22 @@ __FBSDID("$FreeBSD$");
#include <machine/unwind.h>
#include <machine/vmparam.h>
+/*
+ * For atomicity reasons, we demand that pc_curthread is the first
+ * field in the struct pcpu. It allows us to read the pointer with
+ * a single atomic instruction:
+ * ld8 %curthread = [r13]
+ * Otherwise we would first have to calculate the load address and
+ * store the result in a temporary register and that for the load:
+ * add %temp = %offsetof(struct pcpu), r13
+ * ld8 %curthread = [%temp]
+ * A context switch inbetween the add and the ld8 could have the
+ * thread migrate to a different core. In that case, %curthread
+ * would be the thread running on the original core and not actually
+ * the current thread.
+ */
+CTASSERT(offsetof(struct pcpu, pc_curthread) == 0);
+
static SYSCTL_NODE(_hw, OID_AUTO, freq, CTLFLAG_RD, 0, "");
static SYSCTL_NODE(_machdep, OID_AUTO, cpu, CTLFLAG_RD, 0, "");
Modified: head/sys/ia64/ia64/support.S
==============================================================================
--- head/sys/ia64/ia64/support.S Tue Feb 12 17:24:41 2013
(r246714)
+++ head/sys/ia64/ia64/support.S Tue Feb 12 17:38:35 2013
(r246715)
@@ -73,26 +73,25 @@ END(fusufault)
*/
ENTRY(casuword, 3)
{ .mlx
- add r15=PC_CURTHREAD,r13
+ ld8.acq r15=[r13] // r15 = curthread
movl r14=VM_MAXUSER_ADDRESS
;;
}
{ .mib
- ld8 r15=[r15] // r15 = curthread
+ add r15=TD_PCB,r15
cmp.geu p6,p0=in0,r14
(p6) br.dpnt.few 1f
;;
}
{ .mlx
- add r15=TD_PCB,r15
+ ld8 r15=[r15] // r15 = PCB
movl r14=fusufault
;;
}
{ .mmi
- ld8 r15=[r15] // r15 = PCB
- ;;
mov ar.ccv=in1
add r15=PCB_ONFAULT,r15
+ nop 0
;;
}
{ .mmi
@@ -123,12 +122,11 @@ END(casuword)
*/
ENTRY(casuword32, 3)
{ .mlx
- add r15=PC_CURTHREAD,r13
movl r14=VM_MAXUSER_ADDRESS
;;
}
{ .mib
- ld8 r15=[r15] // r15 = curthread
+ ld8.acq r15=[r13] // r15 = curthread
cmp.geu p6,p0=in0,r14
(p6) br.dpnt.few 1f
;;
@@ -177,12 +175,11 @@ END(casuword32)
ENTRY(subyte, 2)
{ .mlx
- add r15=PC_CURTHREAD,r13
movl r14=VM_MAXUSER_ADDRESS
;;
}
{ .mib
- ld8 r15=[r15] // r15 = curthread
+ ld8.acq r15=[r13] // r15 = curthread
cmp.geu p6,p0=in0,r14
(p6) br.dpnt.few 1f
;;
@@ -223,12 +220,11 @@ END(subyte)
ENTRY(suword16, 2)
{ .mlx
- add r15=PC_CURTHREAD,r13
movl r14=VM_MAXUSER_ADDRESS
;;
}
{ .mib
- ld8 r15=[r15] // r15 = curthread
+ ld8.acq r15=[r13] // r15 = curthread
cmp.geu p6,p0=in0,r14
(p6) br.dpnt.few 1f
;;
@@ -269,12 +265,11 @@ END(suword16)
ENTRY(suword32, 2)
{ .mlx
- add r15=PC_CURTHREAD,r13
movl r14=VM_MAXUSER_ADDRESS
;;
}
{ .mib
- ld8 r15=[r15] // r15 = curthread
+ ld8.acq r15=[r13] // r15 = curthread
cmp.geu p6,p0=in0,r14
(p6) br.dpnt.few 1f
;;
@@ -316,12 +311,11 @@ END(suword32)
ENTRY(suword64, 2)
XENTRY(suword)
{ .mlx
- add r15=PC_CURTHREAD,r13
movl r14=VM_MAXUSER_ADDRESS
;;
}
{ .mib
- ld8 r15=[r15] // r15 = curthread
+ ld8.acq r15=[r13] // r15 = curthread
cmp.geu p6,p0=in0,r14
(p6) br.dpnt.few 1f
;;
@@ -370,12 +364,11 @@ END(suword64)
ENTRY(fubyte, 1)
{ .mlx
- add r15=PC_CURTHREAD,r13
movl r14=VM_MAXUSER_ADDRESS
;;
}
{ .mib
- ld8 r15=[r15] // r15 = curthread
+ ld8.acq r15=[r13] // r15 = curthread
cmp.geu p6,p0=in0,r14
(p6) br.dpnt.few 1f
;;
@@ -416,12 +409,11 @@ END(fubyte)
ENTRY(fuword16, 2)
{ .mlx
- add r15=PC_CURTHREAD,r13
movl r14=VM_MAXUSER_ADDRESS
;;
}
{ .mib
- ld8 r15=[r15] // r15 = curthread
+ ld8.acq r15=[r13] // r15 = curthread
cmp.geu p6,p0=in0,r14
(p6) br.dpnt.few 1f
;;
@@ -462,12 +454,11 @@ END(fuword16)
ENTRY(fuword32, 2)
{ .mlx
- add r15=PC_CURTHREAD,r13
movl r14=VM_MAXUSER_ADDRESS
;;
}
{ .mib
- ld8 r15=[r15] // r15 = curthread
+ ld8.acq r15=[r13] // r15 = curthread
cmp.geu p6,p0=in0,r14
(p6) br.dpnt.few 1f
;;
@@ -509,12 +500,11 @@ END(fuword32)
ENTRY(fuword64, 2)
XENTRY(fuword)
{ .mlx
- add r15=PC_CURTHREAD,r13
movl r14=VM_MAXUSER_ADDRESS
;;
}
{ .mib
- ld8 r15=[r15] // r15 = curthread
+ ld8.acq r15=[r13] // r15 = curthread
cmp.geu p6,p0=in0,r14
(p6) br.dpnt.few 1f
;;
@@ -630,10 +620,8 @@ ENTRY(copyinstr, 4)
cmp.geu p6,p0=in0,loc2 // is in user space.
;;
(p6) br.cond.spnt.few copyerr // if it's not, error out.
+ ld8.acq r15=[r13]
movl r14=copyerr // set up fault handler.
- add r15=PC_CURTHREAD,r13 // find curthread
- ;;
- ld8 r15=[r15]
;;
add r15=TD_PCB,r15 // find pcb
;;
@@ -743,10 +731,8 @@ ENTRY(copyin, 3)
cmp.geu p6,p0=in0,loc2 // is in user space.
;;
(p6) br.cond.spnt.few copyerr // if it's not, error out.
+ ld8.acq r15=[r13]
movl r14=copyerr // set up fault handler.
- add r15=PC_CURTHREAD,r13 // find curthread
- ;;
- ld8 r15=[r15]
;;
add r15=TD_PCB,r15 // find pcb
;;
@@ -781,10 +767,8 @@ ENTRY(copyout, 3)
cmp.geu p6,p0=in1,loc2 // is in user space.
;;
(p6) br.cond.spnt.few copyerr // if it's not, error out.
+ ld8.acq r15=[r13]
movl r14=copyerr // set up fault handler.
- add r15=PC_CURTHREAD,r13 // find curthread
- ;;
- ld8 r15=[r15]
;;
add r15=TD_PCB,r15 // find pcb
;;
@@ -806,8 +790,7 @@ ENTRY(copyout, 3)
END(copyout)
ENTRY(copyerr, 0)
- add r14=PC_CURTHREAD,r13 ;; // find curthread
- ld8 r14=[r14] ;;
+ ld8.acq r14=[r13] ;;
add r14=TD_PCB,r14 ;; // curthread->td_addr
ld8 r14=[r14] ;;
add r14=PCB_ONFAULT,r14 ;; //
&curthread->td_pcb->pcb_onfault
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