[Bug dynamic-link/27248] New: Fixes TLS performance degradation after dlopen

[Bug dynamic-link/27248] New: Fixes TLS performance degradation after dlopen

[cd_songkun at hotmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27248

            Bug ID: 27248
           Summary: Fixes TLS performance degradation after dlopen
           Product: glibc
           Version: 2.28
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: dynamic-link
          Assignee: unassigned at sourceware dot org
          Reporter: cd_songkun at hotmail dot com
  Target Milestone: ---

refer:
https://patchwork.ozlabs.org/project/glibc/patch/1465309688.1188.19.camel@mailbox.tu-dresden.de/

Fixes a performance degradation of TLS access in shared libraries which
can be observed after another shared library that uses TLS is loaded
via dl_open. In this case __tls_get_addr takes significant more time.
Once that shared library accesses it's TLS, the performance normalizes.

Attached is a minimal example which gives the following output:

time: 0.723744
after dlopen,
time: 1.789016
after tls access in loaded lib,
time: 0.672865

We do have a use-case where this is actually really significant. I
believe this happens for instance if libstdc++ is loaded implicitly,
but TLS features are not actively used.


We encountered the same problem, but for some reasons, this modification was
aborted and never reached the upstream. Here, I cloned the same problem here.

The patch worked great for our enviroment and performance has some improved.

Test sequence:

    dlopen(with lazy flag)
    (other code)
    create threads
    (other code)
    dlopen(with now flag)

new approach - performace degradation

    .....
    Create threads
    Dlopen(Lazy) /*even if this call is removed same result*/
    Dlopen(Now)

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[Bug dynamic-link/27248] Fixes TLS performance degradation after dlopen

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27248

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |fweimer at redhat dot com
              Flags|                            |security-
         Resolution|---                         |DUPLICATE
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #1 from Florian Weimer <fweimer at redhat dot com> ---
According to the reporter, this is a duplicate of bug 19924.

*** This bug has been marked as a duplicate of bug 19924 ***

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