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Re: TSX lock elision for glibc v10
- From: Andi Kleen <andi at firstfloor dot org>
- To: Rich Felker <dalias at aerifal dot cx>, f at two dot firstfloor dot org
- Cc: Torvald Riegel <triegel at redhat dot com>, Andi Kleen <andi at firstfloor dot org>, libc-alpha at sourceware dot org
- Date: Thu, 13 Jun 2013 22:08:43 +0200
- Subject: Re: TSX lock elision for glibc v10
- References: <1370969416-8337-1-git-send-email-andi at firstfloor dot org> <1371140799 dot 16968 dot 19087 dot camel at triegel dot csb> <20130613193514 dot GE29800 at brightrain dot aerifal dot cx>
> It seems the intent of this patch is to work around the issue by never
> using elision unless it's explicitly requested. However, if I'm not
> mistaken, there's an environment variable to request elision by
> default, and this would DANGEROUSLY break applications using
The "danger" being the enforced deadlock not happening ?
Sorry this whole thing seems like a red herring to me. Even Torvalds
agreed that it is more a bug in the POSIX standard, than anything else.
Obviously it is.
Only requiring opt-in would kill a lot of the benefits from
putting this into glibc. Disabling any nesting would also kill a lot of the
benefit.
We could ask the POSIX comittee for a clarification, but that would
just prevent any chance of getting the feature in 2.18 and get
some real testing.
If we do some real testing and find a real program that is not
completely broken and is affected by this we can reconsider.
But I consider this unlikely.
If you want to break elision completely please do it in your own libc
only. Thanks.
-Andi