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Re: [PATCH v4 4/4] meson: Warn when TCI is selected but TCG backend is a

From: Stefan Weil
Subject: Re: [PATCH v4 4/4] meson: Warn when TCI is selected but TCG backend is available
Date: Mon, 25 Jan 2021 19:58:18 +0100
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.16; rv:78.0) Gecko/20100101 Thunderbird/78.6.1

Am 25.01.21 um 18:05 schrieb Philippe Mathieu-Daudé:

On 1/25/21 5:47 PM, Daniel P. Berrangé wrote:
On Mon, Jan 25, 2021 at 03:45:30PM +0100, Philippe Mathieu-Daudé wrote:
Some new users get confused with 'TCG' and 'TCI', and enable TCI
support expecting to enable TCG.

Emit a warning when native TCG backend is available on the
host architecture, mentioning this is a suboptimal configuration.

Reviewed-by: Stefan Weil <sw@weilnetz.de>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Nitpick, the text printed is completely rewritten from what they
reviewed, so I would probably have dropped their R-b for that
I thought about it, and assumed their review tag was for the logical
change of adding a warning, not particularly the warning content.

I agree this it would have been better to ask them to review again.
Next time I will reset the tags.

You are right, I would not have signed that new text and either used the original text (which was sufficient in my opinion) or used a different one:

Use of the TCG interpretor is not recommended on this host architecture for 
most users because there is a native TCG execution backend available which 
provides substantially better performance.

I have no evidence that TCI is less reliable than TCG, so I would not write that.

And there are people who have good reasons to use TCI. So why should I recommend them to stop that?


Suggested-by: Daniel Berrangé <berrange@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
  meson.build | 7 +++++++
  1 file changed, 7 insertions(+)

diff --git a/meson.build b/meson.build
index 16b2560e7e7..f675c54e636 100644
--- a/meson.build
+++ b/meson.build
@@ -228,6 +228,13 @@
        error('Unsupported CPU @0@, try --enable-tcg-interpreter'.format(cpu))
+  elif get_option('tcg_interpreter')
+    warning('Use of the TCG interpretor is not recommended on this host')
+    warning('architecture. There is a native TCG execution backend available')
+    warning('which provides substantially better performance and reliability.')
+    warning('It is strongly recommended to remove the 
+    warning('configuration option on this architecture to use the native')
+    warning('backend.')

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