On 04/23/2013 01:19 AM, Peter Zijlstra wrote:
On Mon, 2013-04-22 at 08:52 -0400, Rik van Riel wrote:
On 04/22/2013 07:51 AM, Peter Zijlstra wrote:
On Sun, 2013-04-21 at 17:12 -0400, Rik van Riel wrote:
If we always incremented the ticket number by 2 (instead of 1), then
we could use the lower bit of the ticket number as the spinlock.
ISTR that paravirt ticket locks already do that and use the lsb to
indicate the unlock needs to perform wakeups.
Also, since all of this is virt nonsense, shouldn't it live in the
paravirt ticket lock code and leave the native code as is?
Sure, but that is still no reason not to have the virt
implementation be as fast as possible, and share the same
data type as the non-virt implementation.
It has to share the same data-type..
Also, is it guaranteed that the native spin_lock code has
not been called yet before we switch over to the paravirt
functions?
If the native spin_lock code has been called already at
that time, the native code would still need to be modified
to increment the ticket number by 2, so we end up with a
compatible value in each spin lock's .tickets field, and
prevent a deadlock after we switch over to the paravirt
variant.
I thought the stuff already made it upstream, but apparently not; the
lastest posting I'm aware of is here:
https://lkml.org/lkml/2012/5/2/105
That stuff changes the normal ticket increment as well..
pv-ticket spinlock went on hold state, after Avi acked because of:
though on non-PLE, we get a huge advantage, on PLE machine the benefit
was not as impressive (~10% as you stated in email chain) compared to
the complexity of the patches.
So Avi suggested to try PLE improvements first, so they are going upstream.
https://lkml.org/lkml/2012/7/18/247
https://lkml.org/lkml/2013/1/22/104
https://lkml.org/lkml/2013/2/6/345 (on the way in kvm tree)
Current status of PV spinlock:
I have the rebased patches of pv spinlocks and experimenting with latest
kernel.I have
Gleb's irq delivery incorporated into the patch series. But I am
thinknig whether I can
improve some guest side logic in unlock.
I will probably setup a githup and post the link soon.
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