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authorZachary Amsden <zach@vmware.com>2007-02-13 13:26:21 +0100
committerAndi Kleen <andi@basil.nowhere.org>2007-02-13 13:26:21 +0100
commit9226d125d94c7e4964dd41cc5e9ca2ff84091d01 (patch)
tree935d6e80ff843e1d7b54e0fd9386ef2e0d31aa3d /arch/i386/kernel/process.c
parentc119ecce894120790903ef535dac3e105f3d6cde (diff)
downloadblackbird-op-linux-9226d125d94c7e4964dd41cc5e9ca2ff84091d01.tar.gz
blackbird-op-linux-9226d125d94c7e4964dd41cc5e9ca2ff84091d01.zip
[PATCH] i386: paravirt CPU hypercall batching mode
The VMI ROM has a mode where hypercalls can be queued and batched. This turns out to be a significant win during context switch, but must be done at a specific point before side effects to CPU state are visible to subsequent instructions. This is similar to the MMU batching hooks already provided. The same hooks could be used by the Xen backend to implement a context switch multicall. To explain a bit more about lazy modes in the paravirt patches, basically, the idea is that only one of lazy CPU or MMU mode can be active at any given time. Lazy MMU mode is similar to this lazy CPU mode, and allows for batching of multiple PTE updates (say, inside a remap loop), but to avoid keeping some kind of state machine about when to flush cpu or mmu updates, we just allow one or the other to be active. Although there is no real reason a more comprehensive scheme could not be implemented, there is also no demonstrated need for this extra complexity. Signed-off-by: Zachary Amsden <zach@vmware.com> Signed-off-by: Andi Kleen <ak@suse.de> Cc: Andi Kleen <ak@suse.de> Cc: Jeremy Fitzhardinge <jeremy@xensource.com> Cc: Rusty Russell <rusty@rustcorp.com.au> Cc: Chris Wright <chrisw@sous-sol.org> Signed-off-by: Andrew Morton <akpm@osdl.org>
Diffstat (limited to 'arch/i386/kernel/process.c')
-rw-r--r--arch/i386/kernel/process.c25
1 files changed, 17 insertions, 8 deletions
diff --git a/arch/i386/kernel/process.c b/arch/i386/kernel/process.c
index 23ae198dbbc3..cfae587bf7d2 100644
--- a/arch/i386/kernel/process.c
+++ b/arch/i386/kernel/process.c
@@ -670,14 +670,6 @@ struct task_struct fastcall * __switch_to(struct task_struct *prev_p, struct tas
load_TLS(next, cpu);
/*
- * Restore %gs if needed (which is common)
- */
- if (prev->gs | next->gs)
- loadsegment(gs, next->gs);
-
- write_pda(pcurrent, next_p);
-
- /*
* Now maybe handle debug registers and/or IO bitmaps
*/
if (unlikely((task_thread_info(next_p)->flags & _TIF_WORK_CTXSW)
@@ -686,6 +678,15 @@ struct task_struct fastcall * __switch_to(struct task_struct *prev_p, struct tas
disable_tsc(prev_p, next_p);
+ /*
+ * Leave lazy mode, flushing any hypercalls made here.
+ * This must be done before restoring TLS segments so
+ * the GDT and LDT are properly updated, and must be
+ * done before math_state_restore, so the TS bit is up
+ * to date.
+ */
+ arch_leave_lazy_cpu_mode();
+
/* If the task has used fpu the last 5 timeslices, just do a full
* restore of the math state immediately to avoid the trap; the
* chances of needing FPU soon are obviously high now
@@ -693,6 +694,14 @@ struct task_struct fastcall * __switch_to(struct task_struct *prev_p, struct tas
if (next_p->fpu_counter > 5)
math_state_restore();
+ /*
+ * Restore %gs if needed (which is common)
+ */
+ if (prev->gs | next->gs)
+ loadsegment(gs, next->gs);
+
+ write_pda(pcurrent, next_p);
+
return prev_p;
}
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