On Fri, Jun 12, 2015 at 04:15:23PM -0700, Andy Lutomirski wrote:
> > How about this:
> >
> > /*
> > * This should be a memory location in a cache line which is
> > * unlikely to be touched by other processors. The actual
> > * content is immaterial as it is not actually modified in any way.
> > */
> > mwait_ptr = ¤t_thread_info()->flags;
> >
> > and then
> >
> > __monitor(mwait_ptr, 0, 0);
> >
> > We already do this in mwait_play_dead().
> >
> > However, am I even correct in assuming that ->flags won't really be
> > touched as we're doing delay() and nothing pokes into current anyway?
>
> We poke flags remotely, but not frequently enough for this to be a
> problem. However, I don't know that touching current in udelay is
> okay.
>
> How about some read-mostly percpu variable, such as cpu_tss?
Yeah, those look much safer since they're static and are
____cacheline_aligned_in_smp, which is exactly what we want.
I guess we can do
__monitorx(this_cpu_ptr(&cpu_tss), 0, 0);
with a nice comment ontop why we're doing it.
asm looks ok too:
movq $cpu_tss, %rax #, tcp_ptr__
add %gs:this_cpu_off(%rip), %rax # this_cpu_off, tcp_ptr__
xorl %edx, %edx # tmp248
movq %rdx, %rcx # tmp248, tmp248
#APP
# 22 "./arch/x86/include/asm/mwait.h" 1
.byte 0x0f, 0x01, 0xc8;
# 0 "" 2
#NO_APP
Thanks.
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
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