Re: [RFC v3 2/8] cpus: prepare new CpusAccel cpu accelerator interface

From: Paolo Bonzini <pbonzini@redhat.com>
To: "Claudio Fontana" <cfontana@suse.de>,
	"Alex Bennée" <alex.bennee@linaro.org>,
	"Peter Maydell" <peter.maydell@linaro.org>,
	"Philippe Mathieu-Daudé" <philmd@redhat.com>
Cc: Laurent Vivier <lvivier@redhat.com>,
	Thomas Huth <thuth@redhat.com>,
	Eduardo Habkost <ehabkost@redhat.com>,
	Marcelo Tosatti <mtosatti@redhat.com>,
	qemu-devel@nongnu.org, Markus Armbruster <armbru@redhat.com>,
	Roman Bolshakov <r.bolshakov@yadro.com>,
	Pavel Dovgalyuk <dovgaluk@ispras.ru>,
	Wenchao Wang <wenchao.wang@intel.com>,
	haxm-team@intel.com, Sunil Muthuswamy <sunilmut@microsoft.com>,
	Richard Henderson <rth@twiddle.net>,
	Colin Xu <colin.xu@intel.com>
Subject: Re: [RFC v3 2/8] cpus: prepare new CpusAccel cpu accelerator interface
Date: Wed, 5 Aug 2020 10:47:23 +0200	[thread overview]
Message-ID: <5594481c-e887-e48e-630b-c9ebbe542212@redhat.com> (raw)
In-Reply-To: <cf676419-09e6-4c36-c511-031edddf8cba@suse.de>

On 05/08/20 10:40, Claudio Fontana wrote:
>>  #ifdef _WIN32
>> -    /* Eat dummy APC queued by qemu_cpu_kick_thread.  */
>> +    /* Eat dummy APC queued by qemu_cpu_kick_thread. */
>> +    /* NB!!! Should not this be if (hax_enabled)? Is this wrong for whpx? */
>>      if (!tcg_enabled()) {
>>          SleepEx(0, TRUE);
>>      }
> 
> Looking at the history here, I think this should be if (hax_enabled());
> this check was added at a time when whpx did not exist, so I _think_ there might have been an assumption here
> that !tcg_enabled() on windows means actually hax_enabled() for eating this dummy APC.

Yes, that matches the condition under which QueueUserAPC is called in
qemu_cpu_kick_thread.

Paolo

> Probably it does not cause problems, because whpx does not end up calling qemu_wait_io_event,
> instead it calls qemu_wait_io_event_common. But it would be more expressive to use if (hax_enabled()) I think.