linux-kernel - Re: [PATCH 2/2] kunit: enable hardware acceleration when available

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Message-ID: <5d855199-d054-43f2-b209-23bbfa5f6d92@t-8ch.de>
Date: Fri, 1 Nov 2024 15:23:16 +0000
From: Thomas Weißschuh <thomas@...ch.de>
To: Tamir Duberstein <tamird@...il.com>
Cc: Alyssa Ross <hi@...ssa.is>, 
	Brendan Higgins <brendan.higgins@...ux.dev>, David Gow <davidgow@...gle.com>, Rae Moar <rmoar@...gle.com>, 
	linux-kselftest@...r.kernel.org, kunit-dev@...glegroups.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] kunit: enable hardware acceleration when available

On 2024-11-01 10:49:36-0400, Tamir Duberstein wrote:
> On Fri, Nov 1, 2024, 09:52 Alyssa Ross <hi@...ssa.is> wrote:
> >
> > On Fri, Oct 25, 2024 at 05:03:54PM -0400, Tamir Duberstein wrote:
> > > @@ -124,6 +125,29 @@ class LinuxSourceTreeOperationsQemu(LinuxSourceTreeOperations):
> > >                               '-no-reboot',
> > >                               '-nographic',
> > >                               '-serial', self._serial] + self._extra_qemu_params
> > > +             accelerators = {
> > > +                     line.strip()
> > > +                     for line in subprocess.check_output([qemu_binary, "-accel", "help"], text=True).splitlines()
> > > +                     if line and line.islower()
> > > +             }
> > > +             if 'kvm' in accelerators:
> > > +                     try:
> > > +                             with open('/dev/kvm', 'rb+'):
> > > +                                     qemu_command.extend(['-accel', 'kvm'])
> > > +                     except OSError as e:
> > > +                             print(e)
> > > +             elif 'hvf' in accelerators:
> > > +                     try:
> > > +                             for line in subprocess.check_output(['sysctl', 'kern.hv_support'], text=True).splitlines():
> > > +                                     if not line:
> > > +                                             continue
> > > +                                     key, value = line.split(':')
> > > +                                     if key == 'kern.hv_support' and bool(value):
> > > +                                             qemu_command.extend(['-accel', 'hvf'])
> > > +                                             break
> > > +                     except subprocess.CalledProcessError as e:
> > > +                             print(e)
> > > +
> >
> > QEMU supports falling back if one accelerator is not available, if you
> > specify multiple like -accel kvm:tcg.  Couldn't you rely on that rather
> > than re-implementing the availability checks here?
> 
> Have you ever used that? Here's what I get when I try:
> 
> tamird@...irs-MacBook-Pro linux % tools/testing/kunit/kunit.py run
> --arch arm64 --make_options LLVM=1 --raw_output=all
> [10:45:03] Configuring KUnit Kernel ...
> [10:45:03] Building KUnit Kernel ...
> Populating config with:
> $ make ARCH=arm64 O=.kunit olddefconfig LLVM=1
> Building with:
> $ make all compile_commands.json ARCH=arm64 O=.kunit --jobs=12 LLVM=1
> [10:45:07] Starting KUnit Kernel (1/1)...
> Running tests with:
> $ qemu-system-aarch64 -nodefaults -m 1024 -kernel
> .kunit/arch/arm64/boot/Image.gz -append 'kunit.enable=1
> console=ttyAMA0 kunit_shutdown=reboot' -no-reboot -nographic -serial
> stdio -accel kvm:tcg -machine virt -cpu max
> qemu-system-aarch64: -accel kvm:tcg: invalid accelerator kvm:tcg
> 
> The same thing happens with hvf:kvm:tcg or just hvf:tcg.

That syntax is for -machine accel=hvf:kvm:tcg.
But you can also specify -accel multiple times.

> I also can't find this in the documentation.

-accel name[,prop=value[,...]]
      This  is used to enable an accelerator. [..]
      If there is more than one accelerator specified,
      the next one is used if the previous one fails to initialize.

-machine [type=]name[,prop=value[,...]]
      Supported machine properties are:

      accel=accels1[:accels2[:...]]
	     [..]
	     If there is more than one accelerator specified,
	     the next one is used if the  previous one fails to initialize.


Thomas