From: "Alex Bennée" <alex.bennee@linaro.org>
To: Stefan Weil <sw@weilnetz.de>
Cc: "Thomas Huth" <thuth@redhat.com>,
"Daniel P. Berrangé" <berrange@redhat.com>,
"Richard Henderson" <richard.henderson@linaro.org>,
"Philippe Mathieu-Daudé" <f4bug@amsat.org>,
"Wataru Ashihara" <wataash@wataash.com>,
qemu-devel@nongnu.org,
"Wainer dos Santos Moschetta" <wainersm@redhat.com>,
"Philippe Mathieu-Daudé" <philmd@redhat.com>
Subject: Re: [RFC PATCH 2/2] gitlab-ci: Add a job building TCI with Clang
Date: Tue, 26 Jan 2021 17:08:30 +0000 [thread overview]
Message-ID: <878s8fy67l.fsf@linaro.org> (raw)
In-Reply-To: <7e423408-b0e9-2c32-b88b-eb579dd273c5@weilnetz.de>
Stefan Weil <sw@weilnetz.de> writes:
> Am 23.01.21 um 09:59 schrieb Wataru Ashihara:
>
>> Actually I use TCI also on macOS. Like the use case quoted by Philippe,
>> there're even other reasons to use TCI:
>>
>> 1. Learning TCG ops.
>> 2. Debugging QEMU with gdb. e.g. diagnose codegen or stepping into
>> helper functions from tci.c:tcg_qemu_tb_exec().
>> 3. Guest instruction tracing. TCI is faster than TCG or KVM when tracing
>> the guest ops [1]. I guess qira is using TCI for this reason [2].
>>
>> [1]: https://twitter.com/wata_ash/status/1352899988032942080
>> [2]: https://github.com/geohot/qira/blob/v1.3/tracers/qemu_build.sh#L55
>
>
> Yes, TCI can help a lot for debugging, especially also when porting TCG
> to a new host architecture.
>
> If we had binaries which can switch from native to interpreted TCG, it
> could also be a reference implementation used for unit tests, comparing
> the results for each TCG opcode.
>
> Using TCI with profiling like gprof is useful to count the frequency of
> the different TCG opcodes in practical scenarios and can be used to
> detect bottlenecks (and less frequent or unused opcodes) for native TCG,
> too.
FWIW I had a bunch of JIT profiling changes that exposed the TCG op
counts via the JIT profiler. I think I even enabled the op counting by
default because it was fairly lightweight to add.
IOW I think more introspection can be brought into the core TCG code
rather than relying on TCI to achieve it.
--
Alex Bennée
next prev parent reply other threads:[~2021-01-26 17:11 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-10 16:27 [PATCH 0/2] tcg/tci: Fix Clang build Philippe Mathieu-Daudé
2021-01-10 16:27 ` [PATCH 1/2] tcg: Mark more tcg_out*() functions with attribute 'unused' Philippe Mathieu-Daudé
2021-01-10 17:51 ` Richard Henderson
2021-01-10 21:01 ` Philippe Mathieu-Daudé
2021-01-10 16:27 ` [RFC PATCH 2/2] gitlab-ci: Add a job building TCI with Clang Philippe Mathieu-Daudé
2021-01-21 10:08 ` Thomas Huth
2021-01-21 10:32 ` Daniel P. Berrangé
2021-01-21 11:18 ` Philippe Mathieu-Daudé
2021-01-21 11:21 ` Daniel P. Berrangé
2021-01-21 11:48 ` Philippe Mathieu-Daudé
2021-01-21 12:02 ` Daniel P. Berrangé
2021-01-21 13:27 ` Philippe Mathieu-Daudé
2021-01-23 8:59 ` Wataru Ashihara
2021-01-23 10:26 ` Stefan Weil
2021-01-23 13:31 ` Philippe Mathieu-Daudé
2021-01-26 17:08 ` Alex Bennée [this message]
2021-01-26 16:42 ` Alex Bennée
2021-01-21 18:05 ` Wainer dos Santos Moschetta
2021-01-21 18:13 ` Daniel P. Berrangé
2021-01-21 18:28 ` Thomas Huth
2021-01-21 20:46 ` Wainer dos Santos Moschetta
2021-01-22 8:19 ` Thomas Huth
2021-01-26 13:51 ` Wainer dos Santos Moschetta
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