| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | AMatveev(at)bitec(dot)ru |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Jan Wieck <jan(at)wi3ck(dot)info>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Craig Ringer <craig(at)2ndquadrant(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: One process per session lack of sharing |
| Date: | 2016-07-19 18:19:51 |
| Message-ID: | 20160719181951.zzb4jsy2gurehpqb@alap3.anarazel.de |
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| Lists: | pgsql-hackers |
On 2016-07-19 14:18:22 +0300, AMatveev(at)bitec(dot)ru wrote:
> Hi
>
>
> > Using TLS will slow down things noticeably though. So if we were to go
> > there, we'd have to make up for some constant slowdown.
> I can not understand why?
>
> I've read
> https://msdn.microsoft.com/en-us/library/windows/desktop/ms686749(v=vs.85).aspx
> and
> http://david-grs.github.io/tls_performance_overhead_cost_linux/
> """
> The results are quite straightforward: no overhead at all.
> """
>
> 0x0000000000404f40 <+0>: inc DWORD PTR [rip+0x202382]
> vs
> 0x0000000000404f50 <+0>: inc DWORD PTR fs:0xfffffffffffffffc
Not really true IIRC. For one segment offset stuff is encoded more
widely, and for another, it'll generate more uops in many
microarchitectures. Also, we actually *do* qualify for the exception in
the blog you linked above: We have a fair amount of dynamically linked
code.
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