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From: Andres Freund <[email protected]>
To: David Rowley <[email protected]>
Cc: PostgreSQL Development <[email protected]>
Cc: Robert Haas <[email protected]>
Cc: Michael Paquier <[email protected]>
Cc: Tomas Vondra <[email protected]>
Subject:  Re: Avoid stack frame setup in performance critical routines using tail calls
Date: Tue, 20 Jul 2021 00:03:51 -0700
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAApHDvpfr07JBykytxDXLxMjtExgmSKRUaR4dXkAt5xaGumUBA@mail.gmail.com>
References: <[email protected]>
	<CAApHDvpQQc67NbYJkM0GZWVw_wZvUvOuuANCPiOyobV=q1=owA@mail.gmail.com>
	<[email protected]>
	<CAApHDvpfr07JBykytxDXLxMjtExgmSKRUaR4dXkAt5xaGumUBA@mail.gmail.com>

Hi,

On Mon, Jul 19, 2021, at 23:53, David Rowley wrote:
> On Tue, 20 Jul 2021 at 18:17, Andres Freund <[email protected]> wrote:
> > Any chance you could show a `perf annotate AllocSetAlloc` and `perf annotate
> > palloc` from a patched run? And perhaps how high their percentages of the
> > total work are. E.g. using something like
> > perf report -g none|grep -E 'AllocSetAlloc|palloc|MemoryContextAlloc|pfree'
> 
> Sure. See attached.
> 
> David
> 
> Attachments:
> * AllocateSetAlloc.txt
> * palloc.txt
> * percent.txt

Huh, that's interesting. You have some control flow enforcement stuff turned on (the endbr64). And it looks like it has a non zero cost (or maybe it's just skid). Did you enable that intentionally? If not, what compiler/version/distro is it? I think at least on GCC that's -fcf-protection=...

Andres

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