Re: [PATCH v3 00/13] xen: drop hypercall function tables

[Juergen Gross <jgross@xxxxxxxx>]

On 08.03.22 09:50, Jan Beulich wrote:
> On 08.03.2022 09:39, Juergen Gross wrote:
> > On 08.03.22 09:34, Jan Beulich wrote:
> > > On 08.12.2021 16:55, Juergen Gross wrote:
> > > > In order to avoid indirect function calls on the hypercall path as
> > > > much as possible this series is removing the hypercall function tables
> > > > and is replacing the hypercall handler calls via the function array
> > > > by automatically generated call macros.
> > > >
> > > > Another by-product of generating the call macros is the automatic
> > > > generating of the hypercall handler prototypes from the same data base
> > > > which is used to generate the macros.
> > > >
> > > > This has the additional advantage of using type safe calls of the
> > > > handlers and to ensure related handler (e.g. PV and HVM ones) share
> > > > the same prototypes.
> > > >
> > > > A very brief performance test (parallel build of the Xen hypervisor
> > > > in a 6 vcpu guest) showed a very slim improvement (less than 1%) of
> > > > the performance with the patches applied. The test was performed using
> > > > a PV and a PVH guest.
> > > >
> > > > Changes in V2:
> > > > - new patches 6, 14, 15
> > > > - patch 7: support hypercall priorities for faster code
> > > > - comments addressed
> > > >
> > > > Changes in V3:
> > > > - patches 1 and 4 removed as already applied
> > > > - comments addressed
> > > >
> > > > Juergen Gross (13):
> > > >     xen: move do_vcpu_op() to arch specific code
> > > >     xen: harmonize return types of hypercall handlers
> > > >     xen: don't include asm/hypercall.h from C sources
> > > >     xen: include compat/platform.h from hypercall.h
> > > >     xen: generate hypercall interface related code
> > > >     xen: use generated prototypes for hypercall handlers
> > > >     x86/pv-shim: don't modify hypercall table
> > > >     xen/x86: don't use hypercall table for calling compat hypercalls
> > > >     xen/x86: call hypercall handlers via generated macro
> > > >     xen/arm: call hypercall handlers via generated macro
> > > >     xen/x86: add hypercall performance counters for hvm, correct pv
> > > >     xen: drop calls_to_multicall performance counter
> > > >     tools/xenperf: update hypercall names
> > > As it's pretty certain now that parts of this which didn't go in yet will
> > > need re-basing, I'm going to drop this from my waiting-to-be-acked folder,
> > > expecting a v4 instead.
> > Yes, I was planning to spin that up soon.
> >
> > The main remaining question is whether we want to switch the return type
> > of all hypercalls (or at least the ones common to all archs) not
> > requiring to return 64-bit values to "int", as Julien requested.
> Could you remind me of the (sub)thread this was in, to read through the
> justification again? Without recalling any details I guess I'd prefer
> to stick to long for non-compat flavors.
This discussion started with:

https://lists.xen.org/archives/html/xen-devel/2021-12/threads.html#01293


Juergen

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