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From: Steven Rostedt <rostedt@goodmis.org>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Mel Gorman <mgorman@techsingularity.net>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Dirk Hohndel <dirkhh@vmware.com>,
	Jesper Dangaard Brouer <brouer@redhat.com>
Subject: Re: mm, page_alloc: Swap likely to unlikely as code logic is different for next_zones_zonelist()
Date: Fri, 6 Jan 2017 09:41:12 -0500	[thread overview]
Message-ID: <20170106094112.6aae3e5f@gandalf.local.home> (raw)
In-Reply-To: <4414cca4-1a09-ebda-c92b-fa98df1c8e31@suse.cz>

On Fri, 6 Jan 2017 09:00:23 +0100
Vlastimil Babka <vbabka@suse.cz> wrote:

> On 01/06/2017 02:01 AM, Steven Rostedt wrote:
> > Commit 682a3385e773 "mm, page_alloc: inline the fast path of the
> > zonelist iterator" changed how next_zones_zonelist() is called, by
> > adding a static inline function to do the fast path. This function adds:
> > 
> >        if (likely(!nodes && zonelist_zone_idx(z) <= highest_zoneidx))  
> 
> Your profiling stats posted online suggested even this one was wrong:
> 
>           function.file.line         correct 	incorrect 	percent
> next_zones_zonelist.mmzone.h.965    216840653	25415261543	%0.85
> 
> Was it bogus then, or is there other explanation? I have speculated that
> this might be due to multiple cpusets configured in the system.

I didn't have any cpusets configured on either system.

But the number is exaggerated, as it too was affected by the "constant"
optimization by gcc. But when I fixed that, it still gives me about
50%. Probably best just to remove the likely() in that case.

> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>  
> 
> Anyway this makes sense.
> 
> Acked-by: Vlastimil Babka <vbabka@suse.cz>

Thanks!

-- Steve

  reply	other threads:[~2017-01-06 14:42 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-01-06  1:01 mm, page_alloc: Swap likely to unlikely as code logic is different for next_zones_zonelist() Steven Rostedt
2017-01-06  8:00 ` Vlastimil Babka
2017-01-06 14:41   ` Steven Rostedt [this message]
2017-01-06 10:16 ` Mel Gorman

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