It's useless to send reschedule interrupts in such situations. The earliest
point, where schedule() call is possible, is sysret_careful(). But in that
function we directly test TIF_NEED_RESCHED.
So it's possible to get rid of that type of interrupts.
How about this idea? Is set_bit() cheap on x86 machines?
---
arch/x86/kernel/entry_64.S | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index c653dc4..a046ba8 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -409,6 +409,13 @@ GLOBAL(system_call_after_swapgs)
movq_cfi rax,(ORIG_RAX-ARGOFFSET)
movq %rcx,RIP-ARGOFFSET(%rsp)
CFI_REL_OFFSET rip,RIP-ARGOFFSET
+#if !defined(CONFIG_PREEMPT) || !defined(SMP)
+ /*
+ * Tell resched_curr() do not send useless interrupts to us.
+ * Kernel isn't preemptible till sysret_careful() anyway.
+ */
+ LOCK ; bts $TIF_POLLING_NRFLAG,TI_flags+THREAD_INFO(%rsp,RIP-ARGOFFSET)
+#endif
testl $_TIF_WORK_SYSCALL_ENTRY,TI_flags+THREAD_INFO(%rsp,RIP-ARGOFFSET)
jnz tracesys
system_call_fastpath:
@@ -427,6 +434,9 @@ GLOBAL(system_call_after_swapgs)
* Has incomplete stack frame and undefined top of stack.
*/
ret_from_sys_call:
+#if !defined(CONFIG_PREEMPT) || !defined(SMP)
+ LOCK ; btr $TIF_POLLING_NRFLAG,TI_flags+THREAD_INFO(%rsp,RIP-ARGOFFSET)
+#endif
movl $_TIF_ALLWORK_MASK,%edi
/* edi: flagmask */
sysret_check:
--
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