From: Rusty Russell <rusty@rustcorp.com.au>
To: Peter Zijlstra <peterz@infradead.org>, Andi Kleen <ak@linux.intel.com>
Cc: Andi Kleen <andi@firstfloor.org>, x86@kernel.org,
        linux-kernel@vger.kernel.org, mathieu.desnoyers@efficios.com,
        oleg@redhat.com, paulmck@linux.vnet.ibm.com, mingo@kernel.org
Subject: Re: [RFC][PATCH] module: Optimize __module_address() using a latched RB-tree
In-Reply-To: <20150226141256.GY24151@twins.programming.kicks-ass.net>
References: <1424482737-958-1-git-send-email-andi@firstfloor.org> <20150223170436.GC5029@twins.programming.kicks-ass.net> <20150223174340.GD27767@tassilo.jf.intel.com> <20150226114309.GR21418@twins.programming.kicks-ass.net> <20150226141256.GY24151@twins.programming.kicks-ass.net>
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Date: Fri, 27 Feb 2015 22:21:26 +1030
Message-ID: <87mw3zlght.fsf@rustcorp.com.au>
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Peter Zijlstra <peterz@infradead.org> writes:
> On Thu, Feb 26, 2015 at 12:43:09PM +0100, Peter Zijlstra wrote:
>
> Assuming struct module is cacheline aligned, Rusty? from what I can find
> its squirreled away in some data structure:
>
>   mod = (void *)info->sechdrs[info->index.mod].sh_addr
>
> And I can't seem to quickly find its alignment. If its not cacheline
> aligned, can we make it so?

If the ELF says to align it, it will be aligned.  Thus your patch
below should make it Just Work:

> @@ -278,7 +276,7 @@
>  	int (*init)(void);
>  
>  	/* If this is non-NULL, vfree after init() returns */
> -	void *module_init;
> +	void *module_init	____cacheline_aligned;
>  
>  	/* Here is the actual code + data, vfree'd on unload. */
>  	void *module_core;

Cheers,
Rusty.
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