linux-kernel - Re: [PATCH] batman-adv: Deinline batadv_orig_hash

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Message-ID: <20160425141941.GI3381@prodigo>
Date:	Mon, 25 Apr 2016 22:19:41 +0800
From:	Antonio Quartulli <a@...table.cc>
To:	Denys Vlasenko <dvlasenk@...hat.com>
Cc:	Marek Lindner <mareklindner@...mailbox.ch>,
	Simon Wunderlich <sw@...onwunderlich.de>,
	Sven Eckelmann <sven@...fation.org>,
	b.a.t.m.a.n@...ts.open-mesh.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] batman-adv: Deinline batadv_orig_hash_find, save 9024
 bytes

On Mon, Apr 25, 2016 at 03:45:20PM +0200, Denys Vlasenko wrote:
> On 04/25/2016 03:39 PM, Antonio Quartulli wrote:
> > On Mon, Apr 25, 2016 at 03:25:22PM +0200, Denys Vlasenko wrote:
> >> This function compiles to 473 bytes of machine code.
> >> 21 callsites.
> >>
> >>     text     data      bss       dec     hex filename
> >> 95903266 20860288 35991552 152755106 91adba2 vmlinux_before
> >> 95894242 20860288 35991552 152746082 91ab862 vmlinux
> > 
> > Hi Danys,
> > 
> > thanks for your patch. This function is used in a several performance critical
> > code paths (i.e. packet forwarding).
> > 
> > Are we sure we are not losing in performance here?
> 
> Is this a common case?
> 
> 	if (!hash)
> 		return NULL;
> 
> If yes, then we can inline this part only.

Unfortunately not: this case is rather rare at runtime.
These hash tables are initialized when the batman virtual interface is created
and should be freed only upon interface shutdown.

(actually I believe this might be a good candidate for an unlikely())

Cheers,

-- 
Antonio Quartulli

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