On Thu, Jun 08, 2017 at 01:24:44PM +0200, Paolo Bonzini wrote:
>
>
> On 08/06/2017 11:16, Peter Xu wrote:
> >> Oh, I see what you mean: set up the wakeup handler in vmx_vcpu_pi_put
> >> and rely on PI.ON to wake up the sleeping process immediately. That
> >> should be feasible, but overall I like the current pre_block/post_block
> >> structure, and I think it's simpler. The only thing to be careful about
> >> is leaving the IRTE unmodified when scheduling out a blocked VCPU, which
> >> is cleaned up and simplified in patch 3.
> >>
> >> So I understand that the state may seem a bit too complicated as
> >> of this patch, but hopefully the next two make it clearer.
> > After re-read the codes and patches I got the point. Indeed current
> > way should be clearer since pre/post_block are mostly handling NV/DST
> > while pi_load/put are for SN bit. Thanks!
>
> Almost: pi_load handles NDST too. However, I think with patch 3 it's
> clearer how pi_load handles the nesting inside pre_block...post_block.
Yes. The old codes & comments for vmx_vcpu_pi_load() are not very easy
to understand for me.
For patch 3, not sure whether moving clear_sn() upper would be
clearer:
pi_load()
{
if (!pi_test_bit() && vcpu->cpu == cpu)
return;
/* Unconditionally clear SN */
pi_clear_sn();
/*
* If cpu not changed, no need to switch PDST; if WAKEUP, post_block
* will do it for us
*/
if (vcpu->cpu == cpu || nv == WAKEUP)
return;
/*
* Update PDST. Possibly the vcpu thread switched from one cpu to
* another.
*/
do {
...
} while (...)
}
Even, I'm thinking whether we can unconditionally setup PDST only in
pi_load(), then post_block() only needs to handle the NV bit.
(PS. since I'm at here... could I ask why in pi_pre_block we need to
udpate PDST as well? I guess that decides who will run the
wakeup_handler code to kick the vcpu thread, but would that really
matter?)
Thanks,
--
Peter Xu
