Date: Wed, 24 Sep 2014 13:31:22 -0400 From: John Baldwin <jhb@freebsd.org> To: Konstantin Belousov <kostikbel@gmail.com> Cc: adrian@freebsd.org, kib@freebsd.org, freebsd-threads@freebsd.org Subject: Re: sem_post() performance Message-ID: <3994706.9XWGRdTEky@ralph.baldwin.cx> In-Reply-To: <20140924151943.GM8870@kib.kiev.ua> References: <20140921213742.GA46868@stack.nl> <8951456.0ca4t8PBR9@ralph.baldwin.cx> <20140924151943.GM8870@kib.kiev.ua>
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On Wednesday, September 24, 2014 06:19:43 PM Konstantin Belousov wrote: > On Wed, Sep 24, 2014 at 11:04:28AM -0400, John Baldwin wrote: > > On Wednesday, September 24, 2014 05:45:19 PM Konstantin Belousov wrote: > > > I think it is even worse now. If the application linked against FBSD_1.0 > > > (ksem) semaphores implementation runs on the modern host, it cannot > > > share semaphore with modern binary. > > > > Correct. We changed sem_t's ABI hence the compat shims IIRC. > > I mean, that new and old semaphores cannot IPC. Yes. > > > Since this is not considered significant problem, we can avoid compat > > > code there as well. > > By compat code I mean the switch on SEM_VERSION, not symversioning the > libc symbols. Ah, ok. My idea was we can always add that back in later if it becomes an issue (though it would only solve half the problem). > > I think if we leave sem_t alone there is no reason to create new compat > > shims for this change, but the existing FBSD_1.0 versions have to remain > > for people using old binaries, yes? > > Assume we applied new symver to semaphores which use new binary protocol > on the existing sem_t, and, to make it reasonable, use old protocol > when sem_t is accessed by older functions. Then, old binaries cannot > IPC with new binaries, although both are dynamically linked to libc. > IMO this is worse than the problem of different libc versions not > communicating. Yes, I don't think we should bump symver for this change, just change SEM_MAGIC from 'sem1' to 'sem2'. -- John Baldwin
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