Re: [Xen-devel] [PATCH RFC 0/4] Use INVPCID to flush global mappings

[Juergen Gross <jgross@xxxxxxxx>]

On 15/02/18 13:10, Wei Liu wrote:
> I wrote these patches sometime ago to explore PCID and INVPCID. I haven't
> thought through whether how to use both in Xen yet. But seeing Juergen laid 
> out
> his thought on PCID and INVPCID I think some of the patches can be useful.
> 
> I had done some benchmark on the speed in one of my older branch by inserting
> some trace points before and after the flush. It showed that twiddling CR4.PGE
> is 3 to 5 times slower than invpcid.
> 
> This series is in incomplete -- obviously we have CR4.PGE twiddling in a few
> other places. But if you think it is beneficial I can try to convert those
> places as well.

I just did a little experiment by replacing the %cr4 based TLB flush in
Jan's XPTI patches by invpcid, on top of my last XPTI speedup patch (no
fancy ALTERNATIVE, just a plain replacement).

Doing a parallel build of the hypervisor in dom0 showed following data:

                real      user      sys
xpti=no         61.2     167.7     71.9
xpti=yes       112.1     170.1    141.8
 + my speedup  103.0     171.2    131.2
  + invpcid     99.0     170.2    122.0

So system time reduction due to invpcid is quite nice.


Juergen

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