svn commit: r306314 - in stable/11: share/man/man9 sys/amd64/amd64 sys/amd64/include
Konstantin Belousov
kib at FreeBSD.org
Sun Sep 25 17:24:11 UTC 2016
Author: kib
Date: Sun Sep 25 17:24:10 2016
New Revision: 306314
URL: https://svnweb.freebsd.org/changeset/base/306314
Log:
MFC r305692:
Add FPU_KERN_NOCTX flag to the fpu_kern_enter() function on amd64.
Modified:
stable/11/share/man/man9/fpu_kern.9
stable/11/sys/amd64/amd64/fpu.c
stable/11/sys/amd64/include/fpu.h
stable/11/sys/amd64/include/pcb.h
Directory Properties:
stable/11/ (props changed)
Modified: stable/11/share/man/man9/fpu_kern.9
==============================================================================
--- stable/11/share/man/man9/fpu_kern.9 Sun Sep 25 16:50:31 2016 (r306313)
+++ stable/11/share/man/man9/fpu_kern.9 Sun Sep 25 17:24:10 2016 (r306314)
@@ -120,6 +120,16 @@ could be used from both kernel thread an
The
.Fn fpu_kern_leave
function correctly handles such contexts.
+.It Dv FPU_KERN_NOCTX
+Avoid nesting save area.
+If the flag is specified, the
+.Fa ctx
+must be passed as
+.Va NULL .
+The flag should only be used for really short code blocks
+which can be executed in a critical section.
+It avoids the need to allocate the FPU context by the cost
+of increased system latency.
.El
.El
.Pp
Modified: stable/11/sys/amd64/amd64/fpu.c
==============================================================================
--- stable/11/sys/amd64/amd64/fpu.c Sun Sep 25 16:50:31 2016 (r306313)
+++ stable/11/sys/amd64/amd64/fpu.c Sun Sep 25 17:24:10 2016 (r306314)
@@ -633,6 +633,8 @@ fpudna(void)
*/
critical_enter();
+ KASSERT((curpcb->pcb_flags & PCB_FPUNOSAVE) == 0,
+ ("fpudna while in fpu_kern_enter(FPU_KERN_NOCTX)"));
if (PCPU_GET(fpcurthread) == curthread) {
printf("fpudna: fpcurthread == curthread\n");
stop_emulating();
@@ -964,13 +966,39 @@ fpu_kern_enter(struct thread *td, struct
{
struct pcb *pcb;
- KASSERT((ctx->flags & FPU_KERN_CTX_INUSE) == 0, ("using inuse ctx"));
+ pcb = td->td_pcb;
+ KASSERT((flags & FPU_KERN_NOCTX) != 0 || ctx != NULL,
+ ("ctx is required when !FPU_KERN_NOCTX"));
+ KASSERT(ctx == NULL || (ctx->flags & FPU_KERN_CTX_INUSE) == 0,
+ ("using inuse ctx"));
+ KASSERT((pcb->pcb_flags & PCB_FPUNOSAVE) == 0,
+ ("recursive fpu_kern_enter while in PCB_FPUNOSAVE state"));
+ if ((flags & FPU_KERN_NOCTX) != 0) {
+ critical_enter();
+ stop_emulating();
+ if (curthread == PCPU_GET(fpcurthread)) {
+ fpusave(curpcb->pcb_save);
+ PCPU_SET(fpcurthread, NULL);
+ } else {
+ KASSERT(PCPU_GET(fpcurthread) == NULL,
+ ("invalid fpcurthread"));
+ }
+
+ /*
+ * This breaks XSAVEOPT tracker, but
+ * PCB_FPUNOSAVE state is supposed to never need to
+ * save FPU context at all.
+ */
+ fpurestore(fpu_initialstate);
+ set_pcb_flags(pcb, PCB_KERNFPU | PCB_FPUNOSAVE |
+ PCB_FPUINITDONE);
+ return (0);
+ }
if ((flags & FPU_KERN_KTHR) != 0 && is_fpu_kern_thread(0)) {
ctx->flags = FPU_KERN_CTX_DUMMY | FPU_KERN_CTX_INUSE;
return (0);
}
- pcb = td->td_pcb;
KASSERT(!PCB_USER_FPU(pcb) || pcb->pcb_save ==
get_pcb_user_save_pcb(pcb), ("mangled pcb_save"));
ctx->flags = FPU_KERN_CTX_INUSE;
@@ -989,19 +1017,34 @@ fpu_kern_leave(struct thread *td, struct
{
struct pcb *pcb;
- KASSERT((ctx->flags & FPU_KERN_CTX_INUSE) != 0,
- ("leaving not inuse ctx"));
- ctx->flags &= ~FPU_KERN_CTX_INUSE;
-
- if (is_fpu_kern_thread(0) && (ctx->flags & FPU_KERN_CTX_DUMMY) != 0)
- return (0);
- KASSERT((ctx->flags & FPU_KERN_CTX_DUMMY) == 0, ("dummy ctx"));
pcb = td->td_pcb;
- critical_enter();
- if (curthread == PCPU_GET(fpcurthread))
- fpudrop();
- critical_exit();
- pcb->pcb_save = ctx->prev;
+
+ if ((pcb->pcb_flags & PCB_FPUNOSAVE) != 0) {
+ KASSERT(ctx == NULL, ("non-null ctx after FPU_KERN_NOCTX"));
+ KASSERT(PCPU_GET(fpcurthread) == NULL,
+ ("non-NULL fpcurthread for PCB_FPUNOSAVE"));
+ CRITICAL_ASSERT(td);
+
+ clear_pcb_flags(pcb, PCB_FPUNOSAVE | PCB_FPUINITDONE);
+ start_emulating();
+ critical_exit();
+ } else {
+ KASSERT((ctx->flags & FPU_KERN_CTX_INUSE) != 0,
+ ("leaving not inuse ctx"));
+ ctx->flags &= ~FPU_KERN_CTX_INUSE;
+
+ if (is_fpu_kern_thread(0) &&
+ (ctx->flags & FPU_KERN_CTX_DUMMY) != 0)
+ return (0);
+ KASSERT((ctx->flags & FPU_KERN_CTX_DUMMY) == 0,
+ ("dummy ctx"));
+ critical_enter();
+ if (curthread == PCPU_GET(fpcurthread))
+ fpudrop();
+ critical_exit();
+ pcb->pcb_save = ctx->prev;
+ }
+
if (pcb->pcb_save == get_pcb_user_save_pcb(pcb)) {
if ((pcb->pcb_flags & PCB_USERFPUINITDONE) != 0) {
set_pcb_flags(pcb, PCB_FPUINITDONE);
Modified: stable/11/sys/amd64/include/fpu.h
==============================================================================
--- stable/11/sys/amd64/include/fpu.h Sun Sep 25 16:50:31 2016 (r306313)
+++ stable/11/sys/amd64/include/fpu.h Sun Sep 25 17:24:10 2016 (r306314)
@@ -86,6 +86,7 @@ void fpu_save_area_reset(struct savefpu
#define FPU_KERN_NORMAL 0x0000
#define FPU_KERN_NOWAIT 0x0001
#define FPU_KERN_KTHR 0x0002
+#define FPU_KERN_NOCTX 0x0004
#endif
Modified: stable/11/sys/amd64/include/pcb.h
==============================================================================
--- stable/11/sys/amd64/include/pcb.h Sun Sep 25 16:50:31 2016 (r306313)
+++ stable/11/sys/amd64/include/pcb.h Sun Sep 25 17:24:10 2016 (r306314)
@@ -83,6 +83,7 @@ struct pcb {
#define PCB_FPUINITDONE 0x08 /* fpu state is initialized */
#define PCB_USERFPUINITDONE 0x10 /* fpu user state is initialized */
#define PCB_32BIT 0x40 /* process has 32 bit context (segs etc) */
+#define PCB_FPUNOSAVE 0x80 /* no save area for current FPU ctx */
uint16_t pcb_initial_fpucw;
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