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Re: Failure to dlopen libgomp due to static TLS data
- From: Andrew Haley <aph at redhat dot com>
- To: Rich Felker <dalias at libc dot org>, Jakub Jelinek <jakub at redhat dot com>
- Cc: Ulrich Weigand <uweigand at de dot ibm dot com>, libc-alpha at sourceware dot org, gcc at gcc dot gnu dot org, rth at redhat dot com
- Date: Thu, 12 Feb 2015 18:23:12 +0000
- Subject: Re: Failure to dlopen libgomp due to static TLS data
- Authentication-results: sourceware.org; auth=none
- References: <201502121519 dot t1CFJMAe018776 at d03av02 dot boulder dot ibm dot com> <20150212160959 dot GS23507 at brightrain dot aerifal dot cx> <20150212161145 dot GD1746 at tucnak dot redhat dot com> <20150212161617 dot GU23507 at brightrain dot aerifal dot cx>
On 02/12/2015 04:16 PM, Rich Felker wrote:
> On Thu, Feb 12, 2015 at 05:11:45PM +0100, Jakub Jelinek wrote:
>> On Thu, Feb 12, 2015 at 11:09:59AM -0500, Rich Felker wrote:
>>> This usage is supposed to be deprecated. Why isn't libgomp using
>>> TLSDESC/gnu2 model?
>> Because it is significantly slower.
> Seems very unlikely. If storage is allocated in static TLS, TLSDESC is
> almost indistinguishable from IE in performance, even when you run
> artificial benchmarks that do nothing but hammer TLS access. When it
> gets allocated in dynamic TLS, it's somewhat slower, but still
> unlikely to matter for most usage IMO.
The problem I'm seeing is that dynamic TLS is always used even when not
necessary, and that hurts Java (which accesses TLS 128k times in the first
500ms or so of execution). According to lxo his patch fixes that.