From: Richard Henderson <richard.henderson@linaro.org>
To: Stefan Hajnoczi <stefanha@redhat.com>, qemu-devel@nongnu.org
Cc: fweimer@redhat.com, Kevin Wolf <kwolf@redhat.com>,
thuth@redhat.com, qemu-block@nongnu.org,
Fam Zheng <fam@euphon.net>,
sguelton@redhat.com
Subject: Re: [RFC 0/2] tls: add macros for coroutine-safe TLS variables
Date: Mon, 25 Oct 2021 09:16:07 -0700 [thread overview]
Message-ID: <2ca9c094-61e6-54b8-89a8-6dad22514c96@linaro.org> (raw)
In-Reply-To: <20211025140716.166971-1-stefanha@redhat.com>
On 10/25/21 7:07 AM, Stefan Hajnoczi wrote:
> This is a preview of how we can solve the coroutines TLS problem. Coroutines
> re-entered from another thread sometimes see stale TLS values. This happens
> because compilers may cache values across yield points, so a value from the
> previous thread will be used when the coroutine is re-entered in another
> thread.
I'm not thrilled by this, but I guess it does work.
It could be worthwhile to add some inline asm instead for specific hosts -- one
instruction instead of an out-of-line call.
> Serge Guelton developed this technique, see the first patch for details. I'm
> submitting it for discussion before I go ahead with a full conversion of the
> source tree.
>
> Todo:
> - Convert all uses of __thread
> - Extend checkpatch.pl to reject code that uses __thread
Absolutely not. *Perhaps* one or two tls variables which are accessible by coroutines,
but there are plenty that have absolutely no relation. Especially everything related to
user-only execution.
r~
next prev parent reply other threads:[~2021-10-25 16:19 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-25 14:07 [RFC 0/2] tls: add macros for coroutine-safe TLS variables Stefan Hajnoczi
2021-10-25 14:07 ` [RFC 1/2] " Stefan Hajnoczi
2021-10-25 14:14 ` Daniel P. Berrangé
2021-10-26 13:36 ` Stefan Hajnoczi
2021-10-26 13:41 ` Stefan Hajnoczi
2021-10-26 14:10 ` Kevin Wolf
2021-10-26 16:26 ` Stefan Hajnoczi
2021-10-25 17:19 ` Richard Henderson
2021-10-26 13:30 ` Stefan Hajnoczi
2021-10-26 15:32 ` Richard Henderson
2021-10-26 16:27 ` Stefan Hajnoczi
2021-10-25 14:07 ` [RFC 2/2] util/async: replace __thread with QEMU TLS macros Stefan Hajnoczi
2021-10-25 14:20 ` [RFC 0/2] tls: add macros for coroutine-safe TLS variables Philippe Mathieu-Daudé
2021-10-25 16:16 ` Richard Henderson [this message]
2021-10-25 23:27 ` Warner Losh
2021-10-26 13:22 ` Stefan Hajnoczi
2021-10-26 15:10 ` Richard Henderson
2021-10-26 16:34 ` Stefan Hajnoczi
2021-10-26 17:10 ` Richard Henderson
2021-10-26 17:26 ` Thomas Huth
2021-10-26 18:03 ` Richard Henderson
2021-10-27 10:38 ` Kevin Wolf
2021-10-27 12:34 ` Stefan Hajnoczi
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