linux-kernel - Re: [PATCH] direct-io: Deinline submit_page

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Date:	Mon, 14 Mar 2016 10:36:10 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Denys Vlasenko <dvlasenk@...hat.com>
Cc:	Al Viro <viro@...iv.linux.org.uk>, Jens Axboe <axboe@...com>,
	Christoph Hellwig <hch@....de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] direct-io: Deinline submit_page_section, save 5304 bytes

Denys Vlasenko <dvlasenk@...hat.com> writes:

> This function compiles to 2628 bytes, 2 callsites
>
>    text	   data	    bss	    dec	    hex	filename
>   15197	     16	      0	  15213	   3b6d	direct-io.o.before1
>    9655	     16	      0	   9671	   25c7	direct-io.o

And what is the consequence for performance?  If you look at the git
history for this file, you'll find the commit that introduced the
inline:

commit ba253fbf6d3502c54e1ac8792e7ac8290a1f5b8d
Author: Andi Kleen <ak@...ux.intel.com>
Date:   Mon Aug 1 21:38:08 2011 -0700

    direct-io: inline the complete submission path
    
    Add inlines to all the submission path functions. While this increases
    code size it also gives gcc a lot of optimization opportunities
    in this critical hotpath.

    ...

So you're essentially undoing that work.

NAK

Cheers,
Jeff